Aspirin

Our assessments of evidence for each medical benefit fall into one of these categories:

• Strong evidence: consistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results
• Good evidence: significant effects in one large or several mid-sized and well-designed clinical studies ( randomized controlled trialsa study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects with an appropriate placebo or other strong comparison control or observational studies that control for confounds)
• Modest evidence: significant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies), or several small studies aggregated into a meta-analysis
• Preliminary evidence: significant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect
• Weak evidence: one or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects
• Insufficient evidence: preclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example)

Learn more about how we research and rate therapies and practices in How We Rate Therapies ›

Survival

Strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of lower mortality among people with adenocarcinoma using aspirin regularly, particularly among those without metastasis, and with greater benefit among people who smoke

• 50% lower mortality among people with adenocarcinoma, particularly in those without metastasis at diagnosis, with regular aspirin use before and after diagnosis compared to controls, with greater benefit among people who smoke, in a pooled analysis of 5 very large RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹Rothwell PM, Wilson M et al. Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials. Lancet. 2012 Apr 28;379(9826):1591-601.

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of better progression-free survival but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on overall survival among people with cancer as a whole treated with low-dose aspirin during treatment with immune checkpoint inhibitors

• Better progression-free survival but no evidence of an effect on overall survival among people with cancer treated with immune checkpoint inhibitors and low-dose aspirin compared to immune checkpoint inhibitors alone in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 13 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies²Zhang Y, Chen H et al. The effect of concomitant use of statins, NSAIDs, low-dose aspirin, metformin and beta-blockers on outcomes in patients receiving immune checkpoint inhibitors: a systematic review and meta-analysis. Oncoimmunology. 2021 Aug 2;10(1).

Metastasis: strong evidence of moderately less metastasis among people with cancer as a whole treated with aspirin

• Moderately lower metastatic spread among people with cancer treated with low-dose aspirin compared to no aspirin in a meta-analysis of 10 observational studies³Elwood PC, Pickering JE et al. Systematic review update of observational studies further supports aspirin role in cancer treatment: time to share evidence and decision-making with patients? PLoS One. 2018 Sep 25;13(9):e0203957.
• 55% lower risk of metastasis after diagnosis among people treated with aspirin daily compared to controls, with larger benefits among people with colorectal cancer, in a pooled analysis of 5 very large RCTs⁴Rothwell PM, Wilson M et al. Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials. Lancet. 2012 Apr 28;379(9826):1591-601.
• Less distant metastasis among people with prostate, breast, lung, or colorectal cancer treated with aspirin and/or other NSAIDs—predominantly aspirin—before diagnosis (29% lower risk) and after (52% lower risk), and also slightly less lymph node metastasis in a very large meta-analysis of 16 observational studies⁵Zhao X, Xu Z, Li H et al. NSAIDs use and reduced metastasis in cancer patients: results from a meta-analysis. Scientific Reports. 2017 May 12;7(1):1875.

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of moderately lower mortality among people with stage 4 colorectal cancer and normal prediagnosis body mass index treated with aspirin after diagnosis, but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on people with obesity.

• Moderately lower mortality among people with stage 4 colorectal cancer treated with aspirin after diagnosis, but only among people with normal prediagnosis body mass index and not people with obesity, in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁶Davis JS, Chavez JC et al. Association of prediagnosis obesity and postdiagnosis aspirin with survival from stage IV colorectal cancer. JAMA Network Open. 2022 Oct 3;5(10):e2236357.

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of moderately better survival among people aged 65 or older with bladder cancer treated with aspirin

• 33% lower mortality among people with bladder cancer treated with aspirin at least 3 times a week and 25% lower mortality with any aspirin use compared to less use in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁷Loomans-Kropp HA, Pinsky P, Umar A. Evaluation of aspirin use with cancer incidence and survival among older adults in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2021 Jan 4;4(1):e2032072.

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower cancer-specific mortality among people with breast cancer treated with aspirin

• 27% lower cancer-specific mortality among women with breast cancer treated with aspirin after diagnosis compared to no aspirin in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 15 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁸Wu C, Hu M et al. Influence of postdiagnostic aspirin use on clinical outcomes of women with breast cancer: a meta-analysis. Women & Health. 2024 Feb 7;64(2):94-108.
• 21% lower cancer-specific mortality among people with breast cancer treated with aspirin after a cancer diagnosis but no evidence of an effect from use before diagnosis compared to no aspirin or little aspirin use in meta-analyses of 11 observational studies⁹Baker A, Kartsonaki C. Aspirin use and survival among patients with breast cancer: a systematic review and meta-analysis. Oncologist. 2024 Jan 5;29(1):e1-e14.
• 31% lower cancer-specific mortality among people with breast cancer treated with aspirin compared to no aspirin in a very large meta-analysis of 13 observational studies¹⁰Liu J, Zheng F, Yang M, Wu X, Liu A. Effect of aspirin use on survival benefits of breast cancer patients: a meta-analysis. Medicine (Baltimore). 2021 Aug 20;100(33):e26870.
• A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward lower mortality among people with breast cancer treated with low-dose aspirin compared to no aspirin in a large meta-analysis of 14 observational studies¹¹Elwood PC, Pickering JE et al. Systematic review update of observational studies further supports aspirin role in cancer treatment: time to share evidence and decision-making with patients? PLoS One. 2018 Sep 25;13(9):e0203957.

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of distant metastasis among people with breast cancer treated with aspirin and/or other NSAIDs (predominantly aspirin) either before diagnosis (35% lower risk) or after (51% lower risk)

• Lower risk of distant metastasis among people with breast cancer treated with aspirin and/or other NSAIDs—predominantly aspirin—either before diagnosis (35% lower risk) or after (51% lower risk), with weaker benefit for lymph node metastasis, in a meta-analysis of 7 observational studies¹²Zhao X, Xu Z, Li H et al. NSAIDs use and reduced metastasis in cancer patients: results from a meta-analysis. Scientific Reports. 2017 May 12;7(1):1875.

Colorectal cancer as a whole

Survival: good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of better survival among people with colorectal cancer treated with aspirin after diagnosis, with evidence that the effects are stronger among people with PIK3CA mutation or high COX2 expression

• 26% lower cancer-specific mortality (8 studies) among people with colorectal cancer treated with aspirin after a cancer diagnosis compared to no aspirin, with stronger effects among people with PIK3CA mutation (5 studies) or high COX2 expression (2 studies), in meta-analysesstatistical analyses that combine the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹³Mädge JC, Stallmach A, Kleebusch L, Schlattmann P. Meta-analysis of aspirin-guided therapy of colorectal cancer. Journal of Cancer Research and Clinical Oncology. 2022 Jun;148(6):1407-1417.
• 24% lower cancer-specific mortality among people with colorectal cancer treated with aspirin after a cancer diagnosis compared to no aspirin, with stronger effects among people with PIK3CA mutation (4 studies) or high COX2 expression (3 studies), in meta-analyses of observational studies¹⁴Xiao S, Xie W, Fan Y, Zhou L. Timing of aspirin use among patients with colorectal cancer in relation to mortality: a systematic review and meta-analysis. JNCI Cancer Spectrum. 2021 Jul 14;5(5):pkab067.
• 40% lower cancer-specific mortality among people beginning regular aspirin use only after diagnosis compared with no aspirin use either before or after diagnosis in a large observational study¹⁵Figueiredo JC, Jacobs EJ et al. Associations of aspirin and non-aspirin non-steroidal anti-inflammatory drugs with colorectal cancer mortality after diagnosis. NCI: Journal of the National Cancer Institute. 2021 Feb 2:djab008.
• 24% higher 3-year survival, 29% higher 5-year survival, 87% higher partial remission rate, and 43% higher tumor down-staging rate after neoadjuvanttherapy used before a main treatment, such as chemotherapy, radiation therapy, and hormone therapy before surgery chemoradiotherapy before surgery among people with rectal cancer treated with aspirin compared to controls in a meta-analysis of 5 clinical studies¹⁶Wang B, Huang Y. Effect of aspirin use on neoadjuvant chemoradiotherapy for rectal cancer: a meta-analysis with trial sequential analysis. Journal of Cancer Research and Clinical Oncology. 2020 Aug;146(8):2161-2171.
• 32% lower mortality among people with colorectal cancer treated with low-dose aspirin compared to no aspirin in a very large meta-analysis of 29 observational studies¹⁷Elwood PC, Pickering JE et al. Systematic review update of observational studies further supports aspirin role in cancer treatment: time to share evidence and decision-making with patients? PLoS One. 2018 Sep 25;13(9):e0203957.
• Better overall survival among people with mutated-PIK3CA colorectal cancers, but not wild-type PIK3CA, treated with aspirin regularly after diagnosis in a meta-analysis of 3 observational studies¹⁸Mei ZB, Duan CY, Li CB, Cui L, Ogino S. Prognostic role of tumor PIK3CA mutation in colorectal cancer: a systematic review and meta-analysis. Annals of Oncology. 2016 Oct;27(10):1836-48.
• Lower overall mortality and a weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward lower cancer-specific mortality among people with mutated-PIK3CA colorectal cancers, but not wild-type PIK3CA, treated with aspirin after diagnosis in a meta-analysis of observational studies¹⁹Paleari L, Puntoni M et al. PIK3CA mutation, aspirin use after diagnosis and survival of colorectal cancer. a systematic review and meta-analysis of epidemiological studies. Clinical Oncology (Royal College of Radiologists, Great Britain). 2016 May;28(5):317-26.
• 27% lower overall mortality among people with colorectal cancer treated with aspirin compared to no aspirin in a large meta-analysis of 8 observational studies²⁰Ye H, Chen P, Dai W, Zheng Q, Wu F. [Association of long-term oral low-dose aspirin and survival in colorectal cancer: a meta-analysis]. Zhonghua Wei Chang Wai Ke Za Zhi. 2015 Jun;18(6):589-92.
• Substantially longer survival among people with colorectal carcinoma treated with aspirin after diagnosis compared to no use or use only before diagnosis, although non-users of aspirin were more likely to have stage 3 or stage 4 cancer, in a mid-sized observational study²¹Albandar HJ, Markert R, Agrawal S. The relationship between aspirin use and mortality in colorectal cancer. Journal of Gastrointestinal Oncology. 2018 Dec;9(6):1133-1137.

Metastasis: strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of substantially lower risk of metastasis among people with colorectal cancer treated with aspirin, especially after diagnosis and among people who smoke

• 74% lower risk of distant metastasis among people with colorectal cancer with regular aspirin use compared to controls, with greater benefit among people who smoke, in a pooled analysis of 5 very large RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects²²Rothwell PM, Wilson M et al. Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials. Lancet. 2012 Apr 28;379(9826):1591-601.

Special populations 

Hereditary nonpolyposis: preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of slower polyp progression in people with hereditary nonpolyposis colorectal cancer treated with aspirin

• Slower polyp progression in people with hereditary nonpolyposis colorectal cancer treated with aspirin compared to no use in a review of clinical trials²³Wakeman C, Keenan J et al. Chemoprevention of colorectal neoplasia. ANZ Journal of Surgery. 2017 Dec;87(12):E228-E232.

Diabetes: preliminary evidence of substantially better survival among people with type 2 diabetes and colorectal cancer being treated with metformin and using aspirin

• Better cancer-specific survival among people with type 2 diabetes with stage 3 colorectal cancer being treated with metformin and treated with aspirin compared to no aspirin, but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. among people with stage 1 or stage 4 cancer, in a mid-sized observational study²⁴De Monte A, Brunetti D et al. Metformin and aspirin treatment could lead to an improved survival rate for Type 2 diabetic patients with stage II and III colorectal adenocarcinoma relative to non-diabetic patients. Molecular and Clinical Oncology. 2018 Mar;8(3):504-512.

Rectal cancer

Insufficient (conflicting) evidencepreclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example) (this is the CancerChoices definition; other researchers and studies may define this differently) of better tumor response to chemoradiation treatment among people with rectal cancer treated with aspirin

• No evidence of an effect on pathological complete response rate among people with rectal cancer receiving neoadjuvant long-course radiation therapy, with most also receiving concurrent chemotherapy, and treated with aspirin compared to no use in a mid-sized observational study²⁵Hardie C, Jung Y, Jameson M. Effect of statin and aspirin use on toxicity and pathological complete response rate of neo-adjuvant chemoradiation for rectal cancer. Asia-Pacific Journal of Clinical Oncology. 2016 Jun;12(2):167-73.

Gastrointestinal cancer as a whole: good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower cancer-specific mortality among people with digestive tract cancer treated with low-dose aspirin after a cancer diagnosis but no evidence of an effect before diagnosis

• Lower cancer-specific mortality among people with digestive tract cancer including colorectal cancer, esophageal cancer, or gastric cancer treated with low-dose aspirin after a cancer diagnosis but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. before diagnosis compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 13 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies²⁶Wang X, Luo Y, Chen T, Zhang K. Low-dose aspirin use and cancer-specific mortality: a meta-analysis of cohort studies. Journal of Public Health (Oxford, England). 2021 Jun 7;43(2):308-315.

Esophageal cancer: no evidence of an effect on survival among people with esophageal cancer treated with low-dose aspirin after diagnosis in a combined analysis of studies

• No evidence of an effect on survival among people with esophageal or gastrointestinal cancer treated with aspirin after diagnosis compared to no use in a meta-analysis of 18 observational studies²⁷Lin JL, Lin JX et al. Relationship between aspirin use of esophageal, gastric and colorectal cancer patient survival: a meta-analysis. BMC Cancer. 2020 Jul 9;20(1):638.

Liver and biliary tract cancer: good evidence of better survival among people with hepatobiliary tract cancer treated with aspirin regularly after diagnosis

• 41% lower all-cause mortality after liver resection or transarterial chemoembolization among people with liver cancer (hepatocellular carcinoma) treated with aspirin compared to no aspirin in a large meta-analysis of 6 observational studies²⁸Li X, Yu Y, Liu L. Influence of aspirin use on clinical outcomes of patients with hepatocellular carcinoma: a meta-analysis. Clinical Research in Hepatology and Gastroenterology. 2021 Nov;45(6):101545.
• 45% lower mortality among people with hepatobiliary tract cancer treated with aspirin regularly after diagnosis compared to no use in a very large observational study²⁹Liao SF, Koshiol J et al. Postdiagnosis aspirin use associated with decreased biliary tract cancer-specific mortality in a large nationwide cohort. Hepatology. 2021 Oct;74(4):1994-2006.
• Lower mortality among people with biliary tract cancers (37% lower for gallbladder cancer, 29% for cholangiocarcinoma, 66% for ampulla of Vater cancer, and 32% for overlapping biliary tract cancers) treated with aspirin compared to no aspirin, with a larger benefit from postdiagnosis aspirin use than prevalent use, in a large observational study³⁰Jackson SS, Pfeiffer RM et al. Association between aspirin use and biliary tract cancer survival. JAMA Oncology. 2019 Dec 1;5(12):1802-1804. Erratum in: JAMA Oncology. 2019 Dec 1;5(12):1811.
• Longer overall survival and lower bilirubin levels but no evidence of an effect on initial response rate, median time to progression, initial site of progression or fraction of patients dying with disease progression after transarterial chemoembolization or transarterial embolization among people with liver cancer treated with aspirin compared to no aspirin in a mid-sized observational study³¹Boas FE, Brown KT et al. Aspirin is associated with improved liver function after embolization of hepatocellular carcinoma. AJR American Journal of Roentgenology. 2019 Sep;213(3):1-7.

Stomach cancer: no evidence of an effect on survival among people with stomach (gastric) cancer treated with low-dose aspirin after diagnosis in a combined analysis of studies

• No evidence of an effect on survival among people with gastric cancer treated with aspirin after diagnosis compared to no use in a meta-analysis of 18 observational studies³²Lin JL, Lin JX et al. Relationship between aspirin use of esophageal, gastric and colorectal cancer patient survival: a meta-analysis. BMC Cancer. 2020 Jul 9;20(1):638.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on survival among people with head and neck cancer treated with aspirin in a combined analysis of studies

• No evidence of an effect on overall survival among people with head and neck cancer treated with aspirin compared to no aspirin in meta-analysesstatistical analyses that combine the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 7 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies³³Veitz-Keenan A, Silvestre Calle TD, Bergamini M. Limited evidence suggests metformin might be beneficial to reduce head and neck cancer risk and increase overall survival, while any benefit with antiinflammatory drugs is inconsistent. Journal of Evidence-based Dental Practice. 2019 Sep;19(3):298-300; Saka Herrán C, Jané-Salas E, Estrugo Devesa A, López-López J. Protective effects of metformin, statins and anti-inflammatory drugs on head and neck cancer: a systematic review. Oral Oncology. 2018 Oct;85:68-81.

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of better survival and smaller tumor volume among people with head and neck cancer with PIK3CA mutations or amplification using NSAIDs—predominantly aspirin—after diagnosis

• Substantially better cancer-specific survival and smaller tumor volume among people with surgically resected head and neck cancer with PIK3CA mutations or amplification (PIK3CA-altered)—most of whom received chemotherapy, radiotherapy, or both—with any NSAID use (including 73% of people who took aspirin exclusively and another 20% who used aspirin along with other NSAIDs) for 6 months or more after diagnosis, but not among those with wild type PIK3CA, in a mid-sized observational study³⁴Hedberg ML, Peyser ND et al. Use of nonsteroidal anti-inflammatory drugs predicts improved patient survival for PIK3CA-altered head and neck cancer. Journal of Experimental Medicine. 2019 Feb 4;216(2):419-427.

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of longer overall survival among people with inoperable non-small cell lung cancer treated with aspirin

• Longer overall survival among people with inoperable non-small cell lung cancer treated with aspirin compared to no aspirin in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study³⁵Chuang MC, Yang YH et al. The association of aspirin use with overall survival of patients with inoperable non-small cell lung cancer: a retrospective study. BMC Cancer. 2021 Nov 22;21(1):1257.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on response rate, event-free survival, or overall survival after chemoimmunotherapy among people with diffuse large B-cell lymphoma treated with aspirin in a mid-sized study

• No evidence of an effect on response rate, event-free survival, or overall survival after rituximab-based chemoimmunotherapy among people with diffuse large B-cell lymphoma treated with aspirin compared to no aspirin in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study³⁶Koo YX, Tan DSW et al. Effect of concomitant statin, metformin, or aspirin on rituximab treatment for diffuse large B-cell lymphoma. Leukemia & Lymphoma. 2011 Aug;52(8):1509-16.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on overall survival among people with ovarian cancer treated with aspirin in combined analyses of studies

• No evidence of an effect on overall survival among people with ovarian cancer treated with aspirin compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies judged to be free of immortal time bias³⁷Majidi A, Na R, Dixon-Suen S, Jordan SJ, Webb PM. Common medications and survival in women with ovarian cancer: a systematic review and meta-analysis. Gynecological Oncology. 2020 Jun;157(3):678-685.
• No evidence of an effect on overall or progression-free/disease-specific survival among people with ovarian cancer or any subtype of ovarian cancer treated regularly (at least once a week) with aspirin before a cancer diagnosis compared to less or no aspirin in a pooled analysis of 12 observational studies³⁸Dixon SC, Nagle CM et al. Use of common analgesic medications and ovarian cancer survival: results from a pooled analysis in the Ovarian Cancer Association Consortium. British Journal of Cancer. 2017 Apr 25;116(9):1223-1228.

Survival: no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on cancer-specific mortality among people with prostate cancer treated with aspirin in several combined analyses of studies

• No evidence of an effect on cancer-specific mortality among people with prostate cancer treated with aspirin before and/or after diagnosis, at any dose, or for either short or long duration compared to no aspirin in meta-analysesstatistical analyses that combine the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 10 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies³⁹Zhou J, Xia S, Li T, Liu R. Could aspirin be a lifesaver for prostate cancer patients in prostate cancer-specific mortality?: An update systematic review and meta-analysis. BMC Cancer. 2019 Dec 5;19(1):1186.
• No evidence of an effect on cancer-specific mortality among people with prostate cancer treated with aspirin compared to no aspirin in a very large meta-analysis of 14 observational studies⁴⁰Fan LL, Xie CP et al. Aspirin exposure and mortality risk among prostate cancer patients: a systematic review and meta-analysis. BioMed Research International. 2019 Apr 3;2019:9379602.
• No evidence of an effect on cancer-specific mortality among people with prostate cancer treated with low-dose aspirin compared to no aspirin in a large meta-analysis of 16 observational studies⁴¹Elwood PC, Pickering JE et al. Systematic review update of observational studies further supports aspirin role in cancer treatment: time to share evidence and decision-making with patients? PLoS One. 2018 Sep 25;13(9):e0203957.

Metastasis: good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of less distant metastasis among people with prostate cancer treated with aspirin and/or other NSAIDs (predominantly aspirin)

• Less distant metastasis among people with prostate cancer treated with aspirin and/or other NSAIDs (predominantly aspirin) either before diagnosis (13% lower risk) or after (52% lower risk), with weaker benefit for lymph node metastasis, in a very large meta-analysis of 16 observational studies⁴²Zhao X, Xu Z, Li H et al. NSAIDs use and reduced metastasis in cancer patients: results from a meta-analysis. Scientific Reports. 2017 May 12;7(1):1875.
• 77% lower risk of distant metastases after definitive radiation therapy among African American men with prostate cancer treated with aspirin compared to no aspirin in a mid-sized observational study⁴³Osborn VW, Chen SC, Weiner J, Schwartz D, Schreiber D. Impact of aspirin on clinical outcomes for African American men with prostate cancer undergoing radiation. Tumori. 2016 Jan-Feb;102(1):65-70.

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of immune activation against colorectal cancer tumors among people treated with aspirin

• Higher tumor-infiltrating lymphocyte infiltration among people with colorectal cancer treated with aspirin compared to no aspirin in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁴⁴Simoni O, Scarpa M et al; IMMUNOREACT Study Group. IMMUNOREACT 7: Regular aspirin use is associated with immune surveillance activation in colorectal cancer. Cancer. 2024 Jul 1;130(13):2272-2286.

Strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of anti-inflammatory action from aspirin

Aspirin is widely used as an anti-inflammatory agent.⁴⁵Morris T, Stables M et al. Effects of low-dose aspirin on acute inflammatory responses in humans. Journal of Immunology. 2009 Aug 1;183(3):2089-96; Abramson SB. Aspirin: mechanism of action, major toxicities, and use in rheumatic diseases. Up to Date. Apr 21, 2021. Viewed March 23, 2023.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on bladder toxicity during neoadjuvant long-course radiation therapy, with most also receiving concurrent chemotherapy, among people with rectal cancer treated with aspirin

• No evidence of an effect on bladder or rectal toxicity during neoadjuvant long-course radiation therapy, with most also receiving concurrent chemotherapy, among people with rectal cancer treated with aspirin compared to no use in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁴⁶Hardie C, Jung Y, Jameson M. Effect of statin and aspirin use on toxicity and pathological complete response rate of neo-adjuvant chemoradiation for rectal cancer. Asia-Pacific Journal of Clinical Oncology. 2016 Jun;12(2):167-73.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on rectal toxicity during neoadjuvant long-course radiation therapy, with most also receiving concurrent chemotherapy, among people with rectal cancer treated with aspirin

• No evidence of an effect on bladder or rectal toxicity during neoadjuvant long-course radiation therapy, with most also receiving concurrent chemotherapy, among people with rectal cancer treated with aspirin compared to no use in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁴⁷Hardie C, Jung Y, Jameson M. Effect of statin and aspirin use on toxicity and pathological complete response rate of neo-adjuvant chemoradiation for rectal cancer. Asia-Pacific Journal of Clinical Oncology. 2016 Jun;12(2):167-73.

Cardiovascular side effects: preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of fewer vascular disease events, not specific to people with cancer, among people treated with aspirin

• Fewer vascular disease events, including venous thromboembolism among people treated with aspirin in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁴⁸Pulmonary Embolism Prevention (PEP) Trial Collaborative Group. Prevention of pulmonary embolism and deep vein thrombosis with low dose aspirin: Pulmonary Embolism Prevention (PEP) trial. Lancet. 2000 Apr 15;355(9212):1295-302.

Aspirin with codeine: strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of less chronic cancer pain among people using codeine plus aspirin, but see a related commentary about this use for cancer-related pain in How do experts use aspirin? ›

• Less chronic cancer pain among people using a combination of aspirin and codeine—a relatively weak opioid—compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest, and among the top-ranked interventions for global efficacy, superior to stronger opioid formulations in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁴⁹Huang R, Jiang L et al. Comparative efficacy of therapeutics for chronic cancer pain: a Bayesian network meta-analysis. Journal of Clinical Oncology. 2019 Jul 10;37(20):1742-1752.

Cancer mortality: modestsignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) but somewhat conflicting evidence of lower cancer-related mortality among people without cancer at baseline treated with aspirin regularly, especially with use for at least 3 years

• No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on mortality from cancer as a whole during an average of 5.5 years of follow-up among people without cancer at baseline treated with aspirin compared to controls in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁵⁰Haykal T, Barbarawi M et al. Safety and efficacy of aspirin for primary prevention of cancer: a meta-analysis of randomized controlled trials. Journal of Cancer Research and Clinical Oncology. 2019 Jul;145(7):1795-1809.
• No evidence of an effect on overall cancer mortality with a follow-up of at least 12 months among people treated with aspirin compared to no aspirin in a meta-analysis of 12 clinical trials⁵¹Zheng SL, Roddick AJ. Association of aspirin use for primary prevention with cardiovascular events and bleeding events: a systematic review and meta-analysis. JAMA. 2019 Jan 22;321(3):277-287. Erratum in: JAMA. 2019 Jun 11;321(22):2245.
• No evidence of an effect on incidence (6 studies) or mortality (10 studies) of cancer as a whole among adults aged 40 or more treated with aspirin compared to placebo or no aspirin in meta-analyses of clinical studies⁵²Chubak J, Whitlock EP et al. Aspirin for the prevention of cancer incidence and mortality: systematic evidence reviews for the U.S. Preventive Services Task Force. Annals of Internal Medicine. 2016 Jun 21;164(12):814-25.
• 23% lower cancer mortality during an average follow-up of 2.8 years among people without cancer at baseline treated with low-dose aspirin compared to no aspirin, with an average time to benefit of 4 years, in a large meta-analysis of 11 RCTs⁵³Mills EJ, Wu P et al. Low-dose aspirin and cancer mortality: a meta-analysis of randomized trials. American Journal of Medicine. 2012 Jun;125(6):560-7.
• Moderately lower cancer mortality among people without cancer at baseline treated with daily low-dose aspirin, especially for 3 years or longer, compared to controls in a large meta-analysis of 6 RCTs⁵⁴Rothwell PM, Price JF et al. Short-term effects of daily aspirin on cancer incidence, mortality, and non-vascular death: analysis of the time course of risks and benefits in 51 randomised controlled trials. Lancet. 2012 Apr 28;379(9826):1602-12.
• 21% lower cancer-related mortality among people without cancer at baseline treated with aspirin daily for 5 years or longer compared to no use, with the greatest benefit for adenocarcinomas, in a large pooled analysis of randomized trials⁵⁵Rothwell PM, Fowkes FG et al. Effect of daily aspirin on long-term risk of death due to cancer: analysis of individual patient data from randomised trials. Lancet. 2011 Jan 1;377(9759):31-41.
• 35% lower risk of fatal adenocarcinoma with daily aspirin use compared to controls, with greater benefit among people who smoke, but no evidence of an effect on other cancer types in a pooled analysis of 5 very large RCTs⁵⁶Rothwell PM, Wilson M et al. Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials. Lancet. 2012 Apr 28;379(9826):1591-601.

Cancer risk: insufficient evidencepreclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of cancer as a whole among people treated with aspirin

• No evidence of an effect on risk of cancer as a whole during an average of 5.5 years of follow-up among people treated with aspirin compared to controls in a very large meta-analysis of RCTs⁵⁷Haykal T, Barbarawi M et al. Safety and efficacy of aspirin for primary prevention of cancer: a meta-analysis of randomized controlled trials. Journal of Cancer Research and Clinical Oncology. 2019 Jul;145(7):1795-1809.
• No evidence of an effect on overall cancer incidence with a follow-up of at least 12 months among people treated with aspirin compared to no aspirin in a meta-analysis of 12 clinical trials⁵⁸Zheng SL, Roddick AJ. Association of aspirin use for primary prevention with cardiovascular events and bleeding events: a systematic review and meta-analysis. JAMA. 2019 Jan 22;321(3):277-287. Erratum in: JAMA. 2019 Jun 11;321(22):2245.
• 11% lower risk of cancer as a whole among people treated with aspirin compared to no aspirin in a meta-analysis of 218 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁵⁹Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.

Strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of distant metastasis among people without cancer at baseline treated with aspirin regularly, with greater benefit among people who smoke

• 36% lower risk of distant metastasis, either at cancer diagnosis or after, among people without cancer at baseline treated with aspirin regularly compared to controls, with greater benefit among people who smoke, in a pooled analysis of 5 very large RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁶⁰Rothwell PM, Wilson M et al. Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials. Lancet. 2012 Apr 28;379(9826):1591-601.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of bladder cancer among people treated with aspirin in several combined analyses of observational studies; also see cautions about aspirin use in older adults in Safety and precautions ›

• No evidence of an effect on risk of bladder cancer among people aged 65 years or older treated with aspirin compared to no use in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁶¹Loomans-Kropp HA, Pinsky P, Umar A. Evaluation of aspirin use with cancer incidence and survival among older adults in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2021 Jan 4;4(1):e2032072.
• No evidence of an effect on risk of bladder cancer among people treated with aspirin compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 15 observational studies⁶²Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• No evidence of an effect on risk of bladder cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 11 observational studies⁶³Zhang H, Jiang D, Li X. Use of nonsteroidal anti-inflammatory drugs and bladder cancer risk: a meta-analysis of epidemiologic studies. PLoS One. 2013 Jul 19;8(7):e70008.
• No evidence of an effect on risk of bladder cancer among people treated with aspirin compared to no aspirin in a very large combined analysis of 3 observational studies⁶⁴Daugherty SE, Pfeiffer RM et al. Nonsteroidal antiinflammatory drugs and bladder cancer: a pooled analysis. American Journal of Epidemiology. 2011 Apr 1;173(7):721-30.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of brain cancer among people treated with aspirin in combined analyses of observational studies

• A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward lower risk of glioma among people treated with daily aspirin for 6 months or longer compared to no history of daily use in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 6 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁶⁵Amirian ES, Ostrom QT et al. Aspirin, NSAIDs, and glioma risk: original data from the glioma international case-control study and a meta-analysis. Cancer Epidemiology, Biomarkers & Prevention. 2019 Mar;28(3):555-562.
• No evidence of an effect on risk of brain cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 7 observational studies⁶⁶Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• No evidence of an effect on risk of brain cancer among people treated with aspirin, at either low or high doses, compared to no aspirin in meta-analyses of 7 observational studies⁶⁷Liu Y, Lu Y et al. Association between nonsteroidal anti-inflammatory drug use and brain tumour risk: a meta-analysis. British Journal of Clinical Pharmacology. 2014 Jul;78(1):58-68.

Recurrence: good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of recurrence of breast cancer as a whole but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on recurrence among people with high-risk, HER2-negative breast cancer treated with aspirin

• 23% lower risk of recurrence among women with breast cancer treated with aspirin after diagnosis compared to no aspirin in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 15 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁶⁸Wu C, Hu M et al. Influence of postdiagnostic aspirin use on clinical outcomes of women with breast cancer: a meta-analysis. Women & Health. 2024 Feb 7;64(2):94-108.
• No evidence of an effect on risk of recurrence (invasive disease-free survival) among people with high-risk, HER2-negative breast cancer treated with 300 mg aspirin a day compared to placebo in a very large RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁶⁹Chen WY. A randomized phase III, double-blinded, placebo-controlled trial of aspirin as adjuvant therapy for breast cancer (A011502): The Aspirin after Breast Cancer (ABC) Trial. ASCO Plenary Series: February 2022 Session. Journal of Clinical Oncology 2022;40(36_suppl).

Cancer risk: good evidence of slightly lower risk of breast cancer, especially estrogen receptor-positive tumors, among people treated with aspirin, with stronger effects at higher doses and longer duration of use

• 9% lower risk of breast cancer, mainly estrogen receptor-positive tumors, among people treated with more than 6 tablets of aspirin per week compared to no aspirin in a meta-analysis of 28 observational studies⁷⁰Bakierzynska M, Cullinane MC, Redmond HP, Corrigan M. Prophylactic aspirin intake and breast cancer risk; a systematic review and meta-analysis of observational cohort studies. European Journal of Surgical Oncology. 2023 Oct;49(10):106940.
• 8% lower risk of hormone receptor-positive breast cancer, including in postmenopausal women, among people treated with aspirin compared to no aspirin in a large meta-analysis of 42 observational studies⁷¹Ma S, Guo C et al. Aspirin use and risk of breast cancer: a meta-analysis of observational studies from 1989 to 2019. Clinical Breast Cancer. 2021 Dec;21(6):552-565.
• 10% lower risk of breast cancer among people treated with aspirin compared to no aspirin in a large meta-analysis of 33 observational studies⁷²Santucci C, Gallus S, Martinetti M, La Vecchia C, Bosetti C. Aspirin and the risk of nondigestive tract cancers: an updated meta-analysis to 2019. International Journal of Cancer. 2021 Mar 15;148(6):1372-1382.
• No evidence of an effect on risk across all types of breast cancer among people aged 65 years or older treated with aspirin compared to no use in a very large observational study;⁷³Loomans-Kropp HA, Pinsky P, Umar A. Evaluation of aspirin use with cancer incidence and survival among older adults in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2021 Jan 4;4(1):e2032072. also see cautions about aspirin use in older adults in Safety and precautions ›
• A weak trend toward slightly lower risk of breast cancer, with stronger effects at higher doses and longer duration of use, among people treated with aspirin compared to no aspirin in a meta-analysis of 13 observational studies⁷⁴Lu L, Shi L, Zeng J, Wen Z. Aspirin as a potential modality for the chemoprevention of breast cancer: A dose-response meta-analysis of cohort studies from 857,831 participants. Oncotarget. 2017 Jun 20;8(25):40389-40401.
• No evidence of an effect on risk of breast cancer at 16 years after initiation among healthy women aged 45 years or older treated with 100 mg aspirin every other day for 8–10 years compared to placebo in a very large RCT⁷⁵Cook NR, Lee IM, Zhang SM, Moorthy MV, Buring JE. Alternate-day, low-dose aspirin and cancer risk: long-term observational follow-up of a randomized trial. Annals of Internal Medicine. 2013 Jul 16;159(2):77-85.
• 9% lower risk of breast cancer among people treated with aspirin compared to no use, with significant benefits regarding hormone receptor positive tumors, in situ breast tumors, postmenopausal women, and with use more than 4 times a week or for more than 10 years, in a very large meta-analysis of observational studies⁷⁶Cao Y, Tan A. Aspirin might reduce the incidence of breast cancer: an updated meta-analysis of 38 observational studies. Medicine (Baltimore). 2020 Sep 18;99(38):e21917.
• Slightly lower risk of breast cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 33 observational studies⁷⁷Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• Lower risks of cancer mortality and metastatic cancer among people without cancer at baseline treated with aspirin regularly in pooled data from 5 observational studies⁷⁸Chen WY, Holmes MD. Role of aspirin in breast cancer survival. Current Oncology Reports. 2017 Jul;19(7):48.
• Lower risk of in situ breast tumors or hormone receptor-positive tumors, or of breast cancer among postmenopausal women treated with aspirin compared to no use in a meta-analysis of observational studies⁷⁹Zhong S, Chen L et al. Aspirin use and risk of breast cancer: systematic review and meta-analysis of observational studies. Cancer Epidemiology, Biomarkers & Prevention. 2015 Nov;24(11):1645-55.

Recurrence

good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of substantially lower risk of colorectal cancer recurrence, especially among people with colorectal cancer with PIK3CA mutations, although no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on recurrence of advanced neoplasia, among people treated with aspirin regularly

• 49% lower risk of recurrence (better recurrence-free survival) 5 years after adjuvanttreatment applied after initial treatment for cancer, especially to suppress secondary tumor formation chemotherapy among people with colon cancer treated with 5 or more tablets of aspirin per week compared to no use in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁸⁰Ng K, Meyerhardt JA et al. Aspirin and COX-2 inhibitor use in patients with stage III colon cancer. Journal of the National Cancer Institute. 2014 Nov 27;107(1):345.
• 89% lower risk of recurrence among people with colorectal cancer with PIK3CA mutations treated with low-dose aspirin regularly after diagnosis, but no evidence of an effect among people without mutations, compared to no use in an observation within a large trial⁸¹Domingo E, Church DN et al. Evaluation of PIK3CA mutation as a predictor of benefit from nonsteroidal anti-inflammatory drug therapy in colorectal cancer. Journal of Clinical Oncology. 2013 Dec 1;31(34):4297-305.

No evidence of an effect on recurrence of advanced neoplasia among people treated with aspirin regularly

• No evidence of an effect on risk of advanced metachronous neoplasia among people with previous colorectal neoplasia treated with either low-dose or high-dose aspirin compared to placebo in a network meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 14 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁸²Dulai PS, Singh S et al. Chemoprevention of colorectal cancer in individuals with previous colorectal neoplasia: systematic review and network meta-analysis. BMJ. 2016 Dec 5;355:i6188.

Colorectal cancer risk: strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of colorectal cancer among people treated with aspirin regularly, with conflicting evidence regarding whether high doses or low doses offer more protection

• 31% lower risk of colorectal cancer among people treated with the highest doses of aspirin compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest or no aspirin, but no evidence of an effect from low or medium doses in a large meta-analysis of 11 RCTs⁸³Shah D, Di Re A, Toh JWT. Aspirin chemoprevention in colorectal cancer: network meta-analysis of low, moderate, and high doses. British Journal of Surgery. 2023 Nov 9;110(12):1691-1702.
• 18% lower colorectal cancer (CRC) risk (1 very large study) and 23% lower CRC mortality (2 studies) after 20 years but no evidence of an effect on risk of CRC after 10 years or less (4 studies) among people treated with aspirin compared to controls in meta-analyses of RCTs;⁸⁴Guirguis-Blake JM, Evans CV, Perdue LA, Bean SI, Senger CA. Aspirin use to prevent cardiovascular disease and colorectal cancer: updated evidence report and systematic review for the US Preventive Services Task Force. JAMA. 2022 Apr 26;327(16):1585-1597. also see possible evidence from this study of higher colorectal cancer mortality after 5 to 10 years among people treated with aspirin in Safety and precautions ›
• 20% lower risk of proximal colon cancer among people treated with aspirin compared to controls or no use in a meta-analysis of 2 RCTs and 7 observational studies⁸⁵Harewood R, Disney R, Kinross J, von Wagner C, Cross AJ. Medication use and risk of proximal colon cancer: a systematic review of prospective studies with narrative synthesis and meta-analysis. Cancer Causes & Control. 2021 Oct;32(10):1047-1061.
• 15% lower risk of colorectal cancer among people treated with low-dose aspirin and 21% lower risk of colorectal cancer mortality from aspirin as a whole but no evidence of an effect on incidence from aspirin as a whole compared to controls in a meta-analysis of RCTs⁸⁶Ma S, Han T et al. Does aspirin reduce the incidence, recurrence, and mortality of colorectal cancer? A meta-analysis of randomized clinical trials. International Journal of Colorectal Disease. 2021 Aug;36(8):1653-1666.
• 31% lower risk of colorectal cancer-specific mortality and 27% lower risk of distant metastases at the time of diagnosis among people without cancer at baseline treated with aspirin more than 15 times per month long-term before diagnosis in a large observational study⁸⁷Figueiredo JC, Jacobs EJ et al. Associations of aspirin and non-aspirin non-steroidal anti-inflammatory drugs with colorectal cancer mortality after diagnosis. NCI: Journal of the National Cancer Institute. 2021 Feb 2:djab008.
• 27% lower risk of colorectal cancer among people treated with aspirin regularly compared to no use, with more benefit at 325 mg/day compared to 75–100 mg/day in a large meta-analysis of 45 observational studies⁸⁸Bosetti C, Santucci C, Gallus S, Martinetti M, La Vecchia C. Aspirin and the risk of colorectal and other digestive tract cancers: an updated meta-analysis through 2019. Annals of Oncology. 2020;S0923-7534(20)36073-7.
• 29% lower colorectal cancer-related mortality among people aged 65 years and older without cancer at baseline treated with aspirin 3 times a week compared to no use, with even lower mortality among those with body mass index between 25 and 29.9 (overweight), with a follow up of about 12 years in a very large observational study⁸⁹Loomans-Kropp HA, Pinsky P, Cao Y, Chan AT, Umar A. Association of aspirin use with mortality risk among older adult participants in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2019 Dec 2;2(12):e1916729.
• 29% lower risk of colorectal cancer among nonsmokers and 17 to 19% lower risk among smokers, with reducing benefit with more pack-years of smoking, and more benefit among  normal weight or overweight but not obese people, with smaller benefits among either smoking or obese men in a meta-analysis of 12 observational studies⁹⁰Wang X, Chan AT et al. Influence of smoking, body mass index, and other factors on the preventive effect of nonsteroidal anti-inflammatory drugs on colorectal cancer risk. Cancer Research. 2018 Aug 15;78(16):4790-4799.
• 21% lower risk of colorectal cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 39 observational studies⁹¹Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• 64% lower risk of proximal colorectal cancer mortality among people at average risk treated with aspirin compared to guaiac fecal occult blood testing and 64% lower risk compared to flexible sigmoidoscopy, with comparable colorectal cancer incidence among all 3 treatments in a meta-analysis of 15 RCTs⁹²Emilsson L, Holme Ø et al. Systematic review with meta-analysis: the comparative effectiveness of aspirin vs. screening for colorectal cancer prevention. Alimentary Pharmacology & Therapeutics. 2017 Jan;45(2):193-204.
• 40% lower incidence (3 studies) of colorectal cancer among adults aged 40 or more treated with aspirin for more than 10 years and 33% lower colorectal cancer mortality (4 studies) when treated with aspirin for 20 years compared to placebo or no aspirin in large meta-analyses of clinical studies⁹³Chubak J, Whitlock EP et al. Aspirin for the prevention of cancer incidence and mortality: systematic evidence reviews for the U.S. Preventive Services Task Force. Annals of Internal Medicine. 2016 Jun 21;164(12):814-25.

Special populations

People with higher risk due to hereditary, family, or personal history: strong evidence of lower risk of cancer or of polyp progression among people with higher risk due to hereditary, family, or personal history treated with aspirin regularly

• 35% lower risk of colorectal cancer among people with Lynch syndrome, a hereditary condition linked to higher incidence of colorectal cancer, treated with 600 mg aspirin daily compared to placebo with a 10- to 20-year follow up in a large RCT⁹⁴Burn J, Sheth H et al; CAPP2 Investigators. Cancer prevention with aspirin in hereditary colorectal cancer (Lynch syndrome), 10-year follow-up and registry-based 20-year data in the CAPP2 study: a double-blind, randomised, placebo-controlled trial. Lancet. 2020 Jun 13;395(10240):1855-1863.
• Lower risk of colorectal cancer among people treated with aspirin regularly compared to no use, limited to individuals with a specific T allele, in an umbrella review of systematic reviews and meta-analyses of observational studies⁹⁵Yang T, Li X et al. International Journal of Cancer. Gene-environment interactions and colorectal cancer risk: an umbrella review of systematic reviews and meta-analyses of observational studies. 2019 Nov 1;145(9):2315-2329.
• Slower polyp progression in people with hereditary nonpolyposis colorectal cancer treated with aspirin compared to no use in a review of clinical trials⁹⁶Wakeman C, Keenan J et al. Chemoprevention of colorectal neoplasia. ANZ Journal of Surgery. 2017 Dec;87(12):E228-E232.

Older adults: preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of reduced risk only when aspirin use was started before age 65; also see cautions about aspirin use in older adults in Safety and precautions ›

• 20% lower risk of colorectal cancer among people aged 70 or more treated with aspirin regularly compared to irregular use, but only when begun at a younger age, in a large pooled analysis of 2 observational studies⁹⁷Guo CG, Ma W et al. Aspirin use and risk of colorectal cancer among older adults. JAMA Oncology. 2021 Mar 1;7(3):428-435.

People with inflammatory bowel disease: no evidence of an effect on risk of colorectal cancer among people with inflammatory bowel disease treated with aspirin

• No evidence of an effect on risk of colorectal cancer among people with inflammatory bowel disease treated with aspirin compared to no aspirin in a meta-analysis of 3 observational studies⁹⁸Burr NE, Hull MA, Subramanian V. Does aspirin or non-aspirin non-steroidal anti-inflammatory drug use prevent colorectal cancer in inflammatory bowel disease? World Journal of Gastroenterology. 2016 Apr 7;22(13):3679-86.

Genetic markers: good evidence of lower risk of colorectal cancer among white Europeans with specific single nucleotide polymorphisms treated with aspirin

• Lower risk of colorectal cancer among white Europeans with rs6983267, rs11694911, or rs2302615 single nucleotide polymorphisms (SNPs) treated with aspirin compared to no aspirin in a combined analysis of 2 large population-based case-control datasets⁹⁹Sheth H, Northwood E et al. Interaction between polymorphisms in aspirin metabolic pathways, regular aspirin use and colorectal cancer risk: a case-control study in unselected white European populations. PLoS One. 2018 Feb 9;13(2):e0192223.

Adenomas or polyps

Risk of adenomas or polyps: strong evidence of lower risk of colorectal adenomas or advanced lesions among people treated with aspirin, but varying by the duration of aspirin use

• Lower risk of colorectal adenomas but only a weak trend toward fewer advanced lesions at 3 years past baseline, lower risk of advanced lesions but not adenomas at 5 years, and only a weak trend toward lower risk of advanced lesions after more than 5 years among healthy people treated with aspirin daily compared to placebo in a meta-analysis of 11 RCTs¹⁰⁰Ghaddaf AA, Aziz M et al. Influence of aspirin on prevention of colorectal cancer: an updated systematic review and meta-analysis of randomized controlled trials. International Journal of Colorectal Disease. 2021 Aug;36(8):1711-1722.
• 17% lower risk of colorectal colorectal adenomas among people treated with aspirin as a whole compared to controls in a meta-analysis of RCTs¹⁰¹Ma S, Han T et al. Does aspirin reduce the incidence, recurrence, and mortality of colorectal cancer? A meta-analysis of randomized clinical trials. International Journal of Colorectal Disease. 2021 Aug;36(8):1653-1666.
• 19% lower risk of colorectal serrated polyps among people treated with aspirin compared to no use in a meta-analysis of clinical studies¹⁰²Bailie L, Loughrey MB, Coleman HG. Lifestyle risk factors for serrated colorectal polyps: a systematic review and meta-analysis. Gastroenterology. 2017 Jan;152(1):92-104.

Recurrence of adenomas or polyps: strong evidence of lower risk of recurrence of adenomas or polyps among people treated with aspirin, especially low-dose aspirin

• 30% lower risk of recurrence of colorectal adenoma among people treated with low-dose (less than 300 mg per day) aspirin (7 studies) or 24% lower risk with high-dose (300 mg or more per day) compared to placebo, with stronger effects with use longer than 1 year, in a network meta-analysis of RCTs¹⁰³Hoang KD, Chen JH, Huang TW, Kang YN, Chen C. Oral aspirin for preventing colorectal adenoma recurrence: a systematic review and network meta-analysis of randomized controlled trials. PLoS One. 2024 Mar 14;19(3):e0279784.
• Lower recurrence of advanced adenomas among people treated with very low-dose aspirin (100 mg per day or less) compared to low-dose aspirin, to placebo or to calcium and/or vitamin D in a network meta-analysis of 14 RCTs¹⁰⁴Veettil SK, Kew ST et al. Very-low-dose aspirin and surveillance colonoscopy is cost-effective in secondary prevention of colorectal cancer in individuals with advanced adenomas: network meta-analysis and cost-effectiveness analysis. BMC Gastroenterology. 2021 Mar 20;21(1):130.
• 20% lower risk of recurrent colorectal adenomas and 30% lower risk of advanced adenomas among people with previous colorectal adenomas or cancer treated with low-dose (80–160 mg per day) aspirin for 2 to 4 years compared to placebo, but no evidence of an effect with high-dose (300–325 mg per day) aspirin in a meta-analysis of 5 RCTs¹⁰⁵Veettil SK, Lim KG et al. Effects of aspirin and non-aspirin nonsteroidal anti-inflammatory drugs on the incidence of recurrent colorectal adenomas: a systematic review with meta-analysis and trial sequential analysis of randomized clinical trials. BMC Cancer. 2017 Nov 14;17(1):763.
• 27% lower risk of recurrence of colorectal adenoma after 1 year but no evidence of an effect on risk after more than 1 year or on risk of advanced adenoma among people treated with aspirin compared to placebo in a meta-analysis of 5 RCTs¹⁰⁶Zhao TY, Tu J et al. The efficacy of aspirin in preventing the recurrence of colorectal adenoma: a renewed meta-analysis of randomized trials. Asian Pacific Journal of Cancer Prevention. 2016;17(5):2711-7.
• 6.7% absolute lower risk of colorectal adenomas among individuals with a history of these lesions treated with aspirin at various doses compared to no use in a meta-analysis of RCTs¹⁰⁷Cole BF, Logan RF et al. Aspirin for the chemoprevention of colorectal adenomas: meta-analysis of the randomized trials. Journal of the National Cancer Institute. 2009 Feb 18;101(4):256-66.

Gastrointestinal cancer as a whole: modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of a slightly lower risk of gastrointestinal tract cancers among people treated with aspirin regularly

• 15% lower risk of gastrointestinal tract cancers among people treated with aspirin regularly (at least 0.5 to 1.5 standard aspirin tablets a week for at least 6 years) compared to less use in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁰⁸Cao Y, Nishihara R et al. Population-wide impact of long-term use of aspirin and the risk for cancer. JAMA Oncology. 2016 Jun 1;2(6):762-9.

Esophageal cancer

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of adenocarcinoma of the esophagus and gastric cardia or of squamous-cell esophageal cancer among people treated with aspirin regularly

• 39% lower risk of adenocarcinoma of the esophagus and gastric cardia and 33% lower risk of squamous-cell esophageal cancer among people treated with aspirin regularly compared to no use in a large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 13 observational studies¹⁰⁹Bosetti C, Santucci C, Gallus S, Martinetti M, La Vecchia C. Aspirin and the risk of colorectal and other digestive tract cancers: an updated meta-analysis through 2019. Annals of Oncology. 2020;S0923-7534(20)36073-7.
• 25% lower risk of esophageal cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 12 observational studies¹¹⁰Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• Lower risk of esophageal adenocarcinoma among people treated with aspirin compared to no aspirin in a meta-analysis of 9 observational studies¹¹¹Sivarasan N, Smith G. Role of aspirin in chemoprevention of esophageal adenocarcinoma: a meta-analysis. Journal of Digestive Diseases. 2013 May;14(5):222-30.

People with Barrett’s esophagus: modest evidence of moderately lower risk of esophageal adenocarcinoma or high-grade dysplasia among people with Barrett’s esophagus treated with aspirin

• 37% lower risk of esophageal adenocarcinoma or high-grade dysplasia among people with Barrett’s esophagus treated with aspirin compared to no aspirin in a meta-analysis of 4 observational studies¹¹²Zhang S, Zhang XQ et al. Cyclooxygenase inhibitors use is associated with reduced risk of esophageal adenocarcinoma in patients with Barrett’s esophagus: a meta-analysis. British Journal of Cancer. 2014 Apr 29;110(9):2378-88.

Older adults: no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of esophageal cancer among people aged 65 years or older treated with aspirin in a very large study

• No evidence of an effect on risk of esophageal cancer among people aged 65 years or older treated with aspirin compared to no use in a very large observational study¹¹³Loomans-Kropp HA, Pinsky P, Umar A. Evaluation of aspirin use with cancer incidence and survival among older adults in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2021 Jan 4;4(1):e2032072.

Risk of Barrett’s esophagus, a risk factor for esophageal cancer: modest evidence of lower risk of Barrett’s esophagus among people with the highest levels of aspirin use; also see evidence of possibly higher risk of Barrett’s esophagus among people with gastroesophageal reflux symptoms treated with aspirin in Safety and precautions ›

• 30% lower risk of Barrett’s esophagus among people treated with the highest levels of aspirin compared to the lowest in a meta-analysis of 6 observational studies¹¹⁴Zhao Z, Yin Z, Zhang C. Lifestyle interventions can reduce the risk of Barrett’s esophagus: a systematic review and meta-analysis of 62 studies involving 250,157 participants. Cancer Medicine. 2021;10(15):5297-5320.

Liver, bile duct, or gallbladder cancer

Recurrence: good evidence of moderately lower risk of recurrence of liver cancer among people treated with aspirin

• 21% lower risk of recurrence of liver cancer (hepatocellular carcinoma) among people treated with aspirin compared to no aspirin in meta-analysis of 3 observational studies¹¹⁵Ma S, Qu G et al. Does aspirin reduce the incidence, recurrence, and mortality of hepatocellular carcinoma? A GRADE-assessed systematic review and dose-response meta-analysis. European Journal of Clinical Pharmacology. 2023 Jan;79(1):39-61.
• 26% lower risk of recurrence after liver resection or transarterial chemoembolization among people with liver cancer treated with aspirin compared to no aspirin in a large meta-analysis of 6 observational studies¹¹⁶Li X, Yu Y, Liu L. Influence of aspirin use on clinical outcomes of patients with hepatocellular carcinoma: a meta-analysis. Clinical Research in Hepatology and Gastroenterology. 2021 Nov;45(6):101545.
• 50% lower risk of liver cancer recurrence among people treated with aspirin compared to no aspirin in a meta-analysis of 2 observational studies¹¹⁷Tan RZH, Lockart I, Abdel Shaheed C, Danta M. Systematic review with meta-analysis: the effects of non-steroidal anti-inflammatory drugs and anti-platelet therapy on the incidence and recurrence of hepatocellular carcinoma. Alimentary Pharmacology & Therapeutics. 2021 Aug;54(4):356-367.

Cancer incidence: good evidence of lower risk of liver, bile duct, or gallbladder cancer among people treated with aspirin

• 30% lower risk of liver cancer (hepatocellular carcinoma) among people treated with aspirin compared to no aspirin in a very large meta-analysis of 19 observational studies¹¹⁸Wang S, Zuo L et al. The relationship between aspirin consumption and hepatocellular carcinoma: a systematic review and meta-analysis. European Journal of Medical Research. 2023 Jul 8;28(1):226.
• 52% lower risk of liver cancer among people treated with aspirin compared to no aspirin in a very large meta-analysis of 11 observational studies¹¹⁹Zeng RW, Yong JN et al. Meta-analysis: chemoprevention of hepatocellular carcinoma with statins, aspirin and metformin. Alimentary Pharmacology & Therapeutics. 2023 Mar;57(6):600-609.
• 25% lower risk of liver cancer (26 studies) and 28% lower liver cancer mortality (5 studies) among people treated with aspirin compared to no aspirin in meta-analyses of observational studies¹²⁰Ma S, Qu G et al. Does aspirin reduce the incidence, recurrence, and mortality of hepatocellular carcinoma? A GRADE-assessed systematic review and dose-response meta-analysis. European Journal of Clinical Pharmacology. 2023 Jan;79(1):39-61.
• Moderately lower risk of liver cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 18 observational studies¹²¹Wang Y, Wang M et al. Aspirin use and the risk of hepatocellular carcinoma: a meta-analysis. Journal of Clinical Gastroenterology. 2022 Aug 1;56(7):e293-e302.
• 47% lower risk of liver cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 12 observational studies¹²²Liu Y, Ren T, Xu X, Jin J. Association of aspirin and nonaspirin NSAIDs therapy with the incidence risk of hepatocellular carcinoma: a systematic review and meta-analysis on cohort studies. European Journal of Cancer Prevention. 2022 Jan 1;31(1):35-43.
• 49% lower risk of liver cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 7 observational studies¹²³Tan RZH, Lockart I, Abdel Shaheed C, Danta M. Systematic review with meta-analysis: the effects of non-steroidal anti-inflammatory drugs and anti-platelet therapy on the incidence and recurrence of hepatocellular carcinoma. Alimentary Pharmacology & Therapeutics. 2021 Aug;54(4):356-367.
• Substantially lower risk of gallbladder cancer among people treated with using aspirin compared to no use in a large observational study¹²⁴Prasai K, Tella SH et al. Aspirin and statin use and the risk of gallbladder cancer. Cancers (Basel). 2021 Mar 9;13(5):1186.
• 38% lower risk of hepatobiliary tract cancer among people treated with aspirin regularly compared to no use in a large meta-analysis of 5 observational studies¹²⁵Bosetti C, Santucci C, Gallus S, Martinetti M, La Vecchia C. Aspirin and the risk of colorectal and other digestive tract cancers: an updated meta-analysis through 2019. Annals of Oncology. 2020;S0923-7534(20)36073-7.
• 39% lower risk of liver cancer (hepatocellular carcinoma) among people treated with aspirin compared to other people in a very large meta-analysis of observational studies¹²⁶Memel ZN, Arvind A et al. Aspirin use is associated with a reduced incidence of hepatocellular carcinoma: a systematic review and meta-analysis. Hepatology Communications. 2020 Nov 13;5(1).
• 41% lower risk of liver cancer among people treated with aspirin compared to no aspirin in a very large meta-analysis of 8 observational studies¹²⁷Wang S, Yu Y et al. Association of aspirin therapy with risk of hepatocellular carcinoma: a systematic review and dose-response analysis of cohort studies with 2.5 million participants. Pharmacological Research. 2020 Jan;151:104585.
• 44% lower risk of bile duct cancer (cholangiocarcinoma) among people treated with aspirin compared to no use in a very large meta-analysis of observational studies¹²⁸Lapumnuaypol K, Tiu A et al. Effects of aspirin and non-steroidal anti-inflammatory drugs on the risk of cholangiocarcinoma: a meta-analysis. QJM. 2019 Jun 1;112(6):421-427.
• A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward lower risk of hepato-biliary cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 7 observational studies¹²⁹Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.

People with chronic liver disease: good evidence of moderately lower risk of liver cancer among people with chronic liver diseases including viral hepatitis or cirrhosis

• 19% lower risk of liver cancer among people with hepatitis B virus infection and 24% lower risk among people with hepatitis C virus infection among people treated with aspirin compared to no aspirin in a very large meta-analysis of 13 observational studies¹³⁰Wang S, Zuo L et al. The relationship between aspirin consumption and hepatocellular carcinoma: a systematic review and meta-analysis. European Journal of Medical Research. 2023 Jul 8;28(1):226.
• 54% lower risk of liver cancer among people with chronic liver disease (6 studies) and 28% lower risk among people specifically with viral hepatitis (4 studies) treated with aspirin regularly compared to other than regular use in large meta-analyses of observational studies¹³¹Tan JL, Sidhu-Brar S, Woodman R, Chinnaratha MA. Regular aspirin use is associated with a reduced risk of hepatocellular carcinoma (HCC) in chronic liver disease: a systematic review and meta-analysis. Journal of Gastrointestinal Cancer. 2023 Jun;54(2):325-331.
• 31% lower risk of liver cancer among people with hepatitis B (3 studies) and 32% lower risk among people with cirrhosis (5 studies) but no evidence of an effect among people with hepatitis C (6 studies) treated with aspirin compared to no aspirin in large meta-analyses of observational studies¹³²Zeng RW, Yong JN et al. Meta-analysis: chemoprevention of hepatocellular carcinoma with statins, aspirin and metformin. Alimentary Pharmacology & Therapeutics. 2023 Mar;57(6):600-609.
• Moderately lower risk of liver cancer among people with hepatitis B or C virus or chronic liver disease treated with aspirin compared to no aspirin in a meta-analysis of 18 observational studies¹³³Wang Y, Wang M et al. Aspirin use and the risk of hepatocellular carcinoma: a meta-analysis. Journal of Clinical Gastroenterology. 2022 Aug 1;56(7):e293-e302.
• 36% lower risk of liver cancer among people with chronic liver disease treated with 100 mg aspirin per day, and greater benefit than 160 mg per day, compared to no aspirin in a very large meta-analysis of 10 observational studies¹³⁴Yi M, Feng X et al. Aspirin for the prevention of hepatocellular carcinoma: an updated meta-analysis with particular focus on patients with chronic liver disease. European Journal of Clinical Pharmacology. 2022 Apr;78(4):647-656.
• 85% lower risk of liver cancer among people with cirrhosis and 35% lower risk among people with viral hepatitis treated with aspirin compared to no aspirin in a meta-analysis of 12 observational studies¹³⁵Liu Y, Ren T, Xu X, Jin J. Association of aspirin and nonaspirin NSAIDs therapy with the incidence risk of hepatocellular carcinoma: a systematic review and meta-analysis on cohort studies. European Journal of Cancer Prevention. 2022 Jan 1;31(1):35-43.

Stomach cancer: good evidence of lower risk of stomach (gastric) cancer among people treated with aspirin

• 28% lower risk of stomach cancer among people treated with aspirin compared to no aspirin in a very large observational study¹³⁶Seo SI, Park CH et al. Aspirin, metformin, and statin use on the risk of gastric cancer: a nationwide population-based cohort study in Korea with systematic review and meta-analysis. Cancer Medicine. 2022 Feb;11(4):1217-1231.
• 36% lower risk of stomach cancer among people treated with aspirin compared to no aspirin, with stronger benefits from low doses or use longer than 5 years, in a meta-analysis of 21 observational studies¹³⁷Win TT, Aye SN, Lau Chui Fern J, Ong Fei C. Aspirin and reducing risk of gastric cancer: systematic review and meta-analysis of the observational studies. Journal of Gastrointestinal and Liver Diseases. 2020 Jun 3;29(2):191-198.
• 36% lower risk of stomach cancer among people treated with aspirin regularly compared to no aspirin in a large meta-analysis of 14 observational studies¹³⁸Bosetti C, Santucci C, Gallus S, Martinetti M, La Vecchia C. Aspirin and the risk of colorectal and other digestive tract cancers: an updated meta-analysis through 2019. Annals of Oncology. 2020;S0923-7534(20)36073-7.
• 25% lower risk of stomach cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 17 observational studies¹³⁹Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• 36% lower risk of non-cardia stomach cancer but no evidence of an effect on cardia cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 7 observational studies¹⁴⁰Huang XZ, Chen Y et al. Aspirin and non-steroidal anti-inflammatory drugs use reduce gastric cancer risk: a dose-response meta-analysis. Oncotarget. 2017 Jan 17;8(3):4781-4795.

People with head and neck cancer: modest evidence of lower secondary primary cancer, especially esophageal cancer and stomach cancer, among people with head and neck cancer treated with aspirin

• 25% lower risk of secondary primary cancer, especially esophageal cancer and stomach cancer, among people with head and neck cancer treated with aspirin compared to no use in a very large observational study¹⁴¹Lin YS, Yeh CC et al. Aspirin associated with risk reduction of secondary primary cancer for patients with head and neck cancer: a population-based analysis. PLoS One. 2018 Aug 22;13(8):e0199014.

Older adults: no evidence of an effect on risk of esophageal cancer or stomach cancer among individuals aged 65 years or older treated with aspirin in a very large study

• No evidence of an effect on risk of stomach cancer among people aged 65 years or older treated with aspirin compared to no use in a very large observational study¹⁴²Loomans-Kropp HA, Pinsky P, Umar A. Evaluation of aspirin use with cancer incidence and survival among older adults in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2021 Jan 4;4(1):e2032072.

Endometrial cancer: good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of slightly lower risk of endometrial cancer among people treated with aspirin, with benefits mainly among obese women

• 9% lower risk of endometrial cancer among people treated with aspirin compared to no aspirin in a large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 19 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁴³Santucci C, Gallus S, Martinetti M, La Vecchia C, Bosetti C. Aspirin and the risk of nondigestive tract cancers: an updated meta-analysis to 2019. International Journal of Cancer. 2021 Mar 15;148(6):1372-1382.
• Slightly lower risk of endometrial cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 14 observational studies¹⁴⁴Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• 7% lower risk of endometrial cancer among people treated with aspirin compared to no aspirin, with stronger benefits among obese women and for type I endometrial cancer, in a meta-analysis of 13 observational studies¹⁴⁵Zhang D, Bai B, Xi Y, Zhao Y. Can aspirin reduce the risk of endometrial cancer?: A systematic review and meta-analysis of observational studies. International Journal of Gynecological Cancer. 2016 Jul;26(6):1111-20.
• Slightly lower risk of endometrial cancer among people treated with aspirin compared to no aspirin, with stronger benefits among obese women and with high frequency of use, in meta-analyses of 13 observational studies¹⁴⁶Verdoodt F, Friis S, Dehlendorff C, Albieri V, Kjaer SK. Non-steroidal anti-inflammatory drug use and risk of endometrial cancer: a systematic review and meta-analysis of observational studies. Gynecologic Oncology. 2016 Feb;140(2):352-8.
• 13% lower risk of endometrial cancer overall, with 28% lower risk among obese women and no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on non-obese women treated with aspirin compared to no aspirin in a meta-analysis of 9 observational studies¹⁴⁷Neill AS, Nagle CM et al; Australian National Endometrial Cancer Study Group. Aspirin, nonsteroidal anti-inflammatory drugs, paracetamol and risk of endometrial cancer: a case-control study, systematic review and meta-analysis. International Journal of Cancer. 2013 Mar 1;132(5):1146-55.

Uterine cancer: no evidence of an effect on risk of uterine cancer among people aged 65 or older treated with aspirin in a large study; also see cautions about aspirin use in older adults in Safety and precautions ›

• No evidence of an effect on risk of uterine cancer among people aged 65 years or older treated with aspirin compared to no aspirin in a very large observational study¹⁴⁸Loomans-Kropp HA, Pinsky P, Umar A. Evaluation of aspirin use with cancer incidence and survival among older adults in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2021 Jan 4;4(1):e2032072.

Insufficient evidencepreclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example) (this is the CancerChoices definition; other researchers and studies may define this differently) of an effect on risk of head and neck cancer among people treated with aspirin in several combined analyses of studies

• Moderately lower risk of head and neck cancers as a whole and oropharyngeal and laryngeal cancer specifically among people treated with aspirin compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 4 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁴⁹Sassano M, Taborelli M et al. Aspirin intake and head and neck cancer: a pooled analysis within the INHANCE consortium. Head & Neck. 2024 Apr;46(4):926-935.
• No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of head and neck cancer among people treated with aspirin regularly compared to no use in a large meta-analysis of 10 observational studies¹⁵⁰Bosetti C, Santucci C, Gallus S, Martinetti M, La Vecchia C. Aspirin and the risk of colorectal and other digestive tract cancers: an updated meta-analysis through 2019. Annals of Oncology. 2020;S0923-7534(20)36073-7.
• No evidence of an effect on risk of head and neck cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 10 observational studies¹⁵¹Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• No evidence of an effect on risk of head and neck cancer among people treated with aspirin compared to no aspirin in meta-analyses of 7 observational studies¹⁵²Veitz-Keenan A, Silvestre Calle TD, Bergamini M. Limited evidence suggests metformin might be beneficial to reduce head and neck cancer risk and increase overall survival, while any benefit with antiinflammatory drugs is inconsistent. Journal of Evidence-based Dental Practice. 2019 Sep;19(3):298-300; Saka Herrán C, Jané-Salas E, Estrugo Devesa A, López-López J. Protective effects of metformin, statins and anti-inflammatory drugs on head and neck cancer: a systematic review. Oral Oncology. 2018 Oct;85:68-81.
• No evidence of an effect on risk of head and neck cancer among people treated with aspirin compared to no aspirin in a very large meta-analysis of 11 observational studies¹⁵³Tang L, Hu H et al. Association of nonsteroidal anti-inflammatory drugs and aspirin use and the risk of head and neck cancers: a meta-analysis of observational studies. Oncotarget. 2016 Oct 4;7(40):65196-65207.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of kidney cancer (renal cell carcinoma) among people treated with aspirin in 2 combined analyses of studies

See also an increased risk of kidney cancer in another study in Safety and precautions ›

• No evidence of an effect on risk of kidney (renal) cancer among people treated with aspirin compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 15 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁵⁴Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• No evidence of an effect on risk of kidney cancer among people treated with aspirin, regardless of dose or duration, compared to no aspirin in a meta-analysis of 2 observational studies¹⁵⁵Karami S, Daughtery SE et al. Analgesic use and risk of renal cell carcinoma: a case-control, cohort and meta-analytic assessment. International Journal of Cancer. 2016 Aug 1;139(3):584-92.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of leukemia among people treated with aspirin in a combined analysis of studies

• No evidence of an effect on risk of leukemia among people treated with aspirin compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 16 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁵⁶Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of slightly to moderately lower risk of chronic lymphocytic leukemia/small lymphocytic lymphoma among people treated with aspirin

• Slightly lower risk of chronic lymphocytic leukemia/small lymphocytic lymphoma among people treated with aspirin compared to no aspirin in a meta-analysis of 7 observational studies¹⁵⁷Amoori N, Cheraghi M, Fallahzadeh H, Rahmani H. Lack of association between treated with aspirin and development of non-Hodgkins lymphoma: a meta-analysis. Asian Pacific Journal of Cancer Prevention. 2015;16(2):787-92.

Cancer risk: preliminarysignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) and conflicting evidence of lower risk of lung cancer among people treated with aspirin; any benefit may depend on the type of lung cancer, the dose of aspirin, and the age or sex of the people treated with aspirin

• 12% lower risk of lung cancer among people treated with aspirin compared to no aspirin in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 21 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁵⁸Santucci C, Gallus S, Martinetti M, La Vecchia C, Bosetti C. Aspirin and the risk of nondigestive tract cancers: an updated meta-analysis to 2019. International Journal of Cancer. 2021 Mar 15;148(6):1372-1382.
• No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of lung cancer among people aged 65 years or older treated with aspirin compared to no use in a very large observational study;¹⁵⁹Loomans-Kropp HA, Pinsky P, Umar A. Evaluation of aspirin use with cancer incidence and survival among older adults in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2021 Jan 4;4(1):e2032072. also see cautions about aspirin use in older adults in Safety and precautions ›
• Slightly lower risk of lung cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 27 observational studies¹⁶⁰Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• Slightly lower risk of non-small-cell lung cancer but no evidence of an effect on other types of lung cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 20 observational studies¹⁶¹Hochmuth F, Jochem M, Schlattmann P. Meta-analysis of aspirin use and risk of lung cancer shows notable results. European Journal of Cancer Prevention. 2016 Jul;25(4):259-68.
• No clear evidence of an effect on risk of lung cancer among people treated with aspirin compared to no aspirin in a large meta-analysis of 18 observational studies¹⁶²Jiang HY, Huang TB et al. Aspirin use and lung cancer risk: a possible relationship? Evidence from an updated meta-analysis. PLoS One. 2015 Apr 7;10(4):e0122962.
• 43% lower risk of lung cancer among people treated with aspirin compared to no use in a pooled analysis of 2 observational studies¹⁶³Harris RE, Beebe J, Alshafie GA. Reduction in cancer risk by selective and nonselective cyclooxygenase-2 (COX-2) inhibitors. Journal of Experimental Pharmacology. 2012 Aug 10;4:91-6.
• Slightly lower risk of lung cancer among people treated with 7 or more aspirin tablets per week compared to no aspirin but no evidence of an effect at smaller doses in a large meta-analysis of 19 observational studies¹⁶⁴Xu J, Yin Z et al. Meta-analysis on the association between nonsteroidal anti-inflammatory drug use and lung cancer risk. Clinical Lung Cancer. 2012 Jan;13(1):44-51.
• 27% lower risk of lung cancer among men treated with aspirin compared to no nonsteroidal anti-inflammatory drugs (NSAIDS), but no evidence of an effect among women in a meta-analysis of 8 observational studies¹⁶⁵McCormack VA, Hung RJ. Aspirin and NSAID use and lung cancer risk: a pooled analysis in the International Lung Cancer Consortium (ILCCO). Cancer Causes and Control. 2011 Dec;22(12):1709-20.
• No evidence of an effect on risk of lung cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 7 high quality observational studies¹⁶⁶Oh SW, Myung SK, Park JY, Lee CM, Kwon HT; Korean Meta-analysis (KORMA) Study Group. Aspirin use and risk for lung cancer: a meta-analysis. Annals of Oncology. 2011 Nov;22(11):2456-2465.

Lymphoma as a whole: no evidence of an effect on risk of lymphoma among people treated with aspirin in a combined analysis of studies

• No evidence of an effect on risk of lymphoma among people treated with aspirin compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 16 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁶⁷Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.

Hodgkin lymphoma: no evidence of an effect on risk of Hodgkin lymphoma among people treated with low-dose aspirin

• No evidence of an effect on risk of Hodgkin lymphoma among people treated with low-dose  aspirin compared to never or rare use in a very large observational study¹⁶⁸Chang ET, Frøslev T, Sørensen HT, Pedersen L. A nationwide study of aspirin, other non-steroidal anti-inflammatory drugs, and Hodgkin lymphoma risk in Denmark. British Journal of Cancer. 2011 Nov 22;105(11):1776-82.

Non-Hodgkin lymphoma

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of slightly lower risk of non-Hodgkin lymphoma among women treated with aspirin but no evidence of an effect across both men and women

• Slightly lower risk of non-Hodgkin lymphoma among women treated with aspirin compared to no aspirin, but no evidence of an effect among men in a meta-analysis of 7 observational studies¹⁶⁹Amoori N, Cheraghi M, Fallahzadeh H, Rahmani H. Lack of association between treated with aspirin and development of non-Hodgkins lymphoma: a meta-analysis. Asian Pacific Journal of Cancer Prevention. 2015;16(2):787-92.
• No evidence of an effect on all non-Hodgkin lymphomas combined among people treated with aspirin compared to no aspirin in a meta-analysis of 17 observational studies¹⁷⁰Ye X, Casaclang N, Mahmud SM. Use of non-steroidal anti-inflammatory drugs and risk of non-Hodgkin lymphoma: a systematic review and meta-analysis. Hematological Oncology. 2015 Dec;33(4):176-86.

Modest evidence of slightly to moderately lower risk of chronic lymphocytic leukemia/small lymphocytic lymphoma but no evidence of an effect on follicular lymphoma or large B-cell lymphoma among people treated with aspirin

• Slightly lower risk of chronic lymphocytic leukemia/small lymphocytic lymphoma but no evidence of an effect on follicular lymphoma or large B-cell lymphoma among people treated with aspirin compared to no aspirin in a meta-analysis of 7 observational studies¹⁷¹Amoori N, Cheraghi M, Fallahzadeh H, Rahmani H. Lack of association between treated with aspirin and development of non-Hodgkins lymphoma: a meta-analysis. Asian Pacific Journal of Cancer Prevention. 2015;16(2):787-92.

Skin cancer as a whole: weak evidence of slightly lower risk of skin cancer among people treated with aspirin

• A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward a slightly lower risk of skin cancer among people treated with aspirin compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 14 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁷²Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.

Basal cell carcinoma: preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of slightly lower risk of basal cell carcinoma among people treated with aspirin, with more benefits among people with a history of skin cancers or a high prevalence of actinic keratoses

• Slightly lower risk of basal cell carcinoma among people treated with aspirin compared to no aspirin, with more benefits among people with a history of skin cancers or a high prevalence of actinic keratoses, in a meta-analysis of 10 observational studies and 1 RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁷³Muranushi C, Olsen CM, Green AC, Pandeya N. Can oral nonsteroidal antiinflammatory drugs play a role in the prevention of basal cell carcinoma? A systematic review and metaanalysis. Journal of the American Academy of Dermatology. 2016 Jan;74(1):108-119.e1.

Cutaneous squamous cell carcinoma: weak evidence of lower risk of cutaneous squamous cell carcinoma among people treated with aspirin

• A weak trend toward lower risk of cutaneous squamous cell carcinoma among people treated with aspirin compared to no aspirin in a meta-analysis of 9 observational studies¹⁷⁴Muranushi C, Olsen CM, Pandeya N, Green AC. Aspirin and nonsteroidal anti-inflammatory drugs can prevent cutaneous squamous cell carcinoma: a systematic review and meta-analysis. Journal of Investigative Dermatology. 2015 Apr;135(4):975-983.

Melanoma: insufficient evidence of an effect on risk of melanoma among people treated with aspirin

• No evidence of an effect on risk of melanoma among people treated with aspirin compared to no aspirin in a very large meta-analysis of 10 observational studies¹⁷⁵Hu H, Xie Y, Yang G, Jian C, Deng Y. Nonsteroidal anti-inflammatory drug use and the risk of melanoma: a meta-analysis. European Journal of Cancer Prevention. 2014 Jan;23(1):62-8.
• 20% lower risk of melanoma among people treated with aspirin compared to no aspirin in a very large meta-analysis of 6 case-control observational studies but no evidence of an effect on risk in a very large meta-analysis of 6 cohort observational studies or a very large RCT¹⁷⁶Li S, Liu Y et al. Association between non-steroidal anti-inflammatory drug use and melanoma risk: a meta-analysis of 13 studies. Cancer Causes and Control. 2013 Aug;24(8):1505-16.

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of slightly lower risk of ovarian cancer among people treated with aspirin, including people with risk factors for ovarian cancer

• 13% lower risk of ovarian cancer among people with any cancer risk factors other than endometriosis treated with aspirin frequently (6 or more days per week) compared to less frequent use in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 17 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁷⁷Hurwitz LM, Townsend MK et al. Modification of the association between frequent aspirin use and ovarian cancer risk: a meta-analysis using individual-level data from two ovarian cancer consortia. Journal of Clinical Oncology. 2022 Jul 22:JCO2101900.
• 9% lower risk of ovarian cancer among people treated with aspirin compared to no aspirin in a large meta-analysis of 22 observational studies¹⁷⁸Santucci C, Gallus S, Martinetti M, La Vecchia C, Bosetti C. Aspirin and the risk of nondigestive tract cancers: an updated meta-analysis to 2019. International Journal of Cancer. 2021 Mar 15;148(6):1372-1382.
• 11% lower risk of ovarian cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 21 observational studies¹⁷⁹Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• 11% lower risk of ovarian cancer among people treated with aspirin compared to no aspirin, with possibly higher benefits from higher doses or longer duration of use, in a meta-analysis of 23 observational studies¹⁸⁰Zhang D, Bai B, Xi Y, Wang T, Zhao Y. Is aspirin use associated with a decreased risk of ovarian cancer? A systematic review and meta-analysis of observational studies with dose-response analysis. Gynecologic Oncology. 2016 Aug;142(2):368-77.
• 9% lower risk of ovarian cancer among people treated with aspirin compared to no aspirin, with stronger benefits from daily use or low-dose (less than 100 mg) aspirin, in a meta-analysis of 12 observational studies¹⁸¹Trabert B, Ness RB et al. Aspirin, nonaspirin nonsteroidal anti-inflammatory drug, and acetaminophen use and risk of invasive epithelial ovarian cancer: a pooled analysis in the Ovarian Cancer Association Consortium. Journal of the National Cancer Institute. 2014 Feb;106(2):djt431.

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of moderately lower risk of pancreatic cancer among people treated with aspirin

• 22% lower risk of pancreatic cancer among people treated with aspirin regularly compared to no use in a large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 15 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁸²Bosetti C, Santucci C, Gallus S, Martinetti M, La Vecchia C. Aspirin and the risk of colorectal and other digestive tract cancers: an updated meta-analysis through 2019. Annals of Oncology. 2020;S0923-7534(20)36073-7.
• 18% lower risk of pancreatic cancer (10 studies) but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on pancreatic cancer mortality among people without cancer at baseline (2 studies) treated with aspirin compared to no aspirin in meta-analyses of observational studies¹⁸³Sun J, Li Y, Liu L, Jiang Z, Liu G. Aspirin use and pancreatic cancer risk: a systematic review of observational studies. Medicine (Baltimore). 2019 Dec;98(51):e18033.
• 20% lower risk of pancreatic cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 14 observational studies¹⁸⁴Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• 23% lower risk of pancreatic cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 8 observational studies¹⁸⁵Zhang YP, Wan YD, Sun YL, Li J, Zhu RT. Aspirin might reduce the incidence of pancreatic cancer: a meta-analysis of observational studies. Scientific Reports. 2015 Oct 21;5:15460.
• A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward slightly lower risk of pancreatic cancer among people treated with high-dose aspirin compared to lower doses, but no evidence of an effect from low-dose aspirin, in a very large meta-analysis of 9 observational studies and 1 RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁸⁶Cui XJ, He Q et al. High-dose aspirin consumption contributes to decreased risk for pancreatic cancer in a systematic review and meta-analysis. Pancreas. 2014 Jan;43(1):135-40.

No evidence of an effect on risk of pancreatic cancer among older adults treated with aspirin; see cautions about aspirin use in older adults in Safety and precautions ›

• No evidence of an effect on risk of pancreatic cancer among people aged 65 years or older treated with aspirin compared to no use in a large observational study¹⁸⁷Loomans-Kropp HA, Pinsky P, Umar A. Evaluation of aspirin use with cancer incidence and survival among older adults in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. JAMA Network Open. 2021 Jan 4;4(1):e2032072.

Recurrence: preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of moderately lower risk of biochemical recurrence after definitive radiation therapy among African American men with prostate cancer treated with aspirin

• 44% lower risk of biochemical recurrence after definitive radiation therapy among African American men with prostate cancer treated with aspirin compared to no aspirin in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁸⁸Osborn VW, Chen SC, Weiner J, Schwartz D, Schreiber D. Impact of aspirin on clinical outcomes for African American men with prostate cancer undergoing radiation. Tumori. 2016 Jan-Feb;102(1):65-70.

Cancer risk: good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of slightly lower risk of prostate cancer, especially of advanced or lethal cancer, among people treated with aspirin

• Slightly lower incidence (49 studies) and mortality from prostate cancer among people without cancer at baseline (18 studies) treated with aspirin compared to no aspirin in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of observational studies and RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁸⁹Ma S, Xia W et al. Effect of aspirin on incidence, recurrence, and mortality in prostate cancer patients: integrating evidence from randomized controlled trials and real-world studies. European Journal of Clinical Pharmacology. 2023 Nov;79(11):1475-1503.
• 7% lower risk of prostate cancer among people treated with aspirin compared to no aspirin in a large meta-analysis of 30 observational studies¹⁹⁰Santucci C, Gallus S, Martinetti M, La Vecchia C, Bosetti C. Aspirin and the risk of nondigestive tract cancers: an updated meta-analysis to 2019. International Journal of Cancer. 2021 Mar 15;148(6):1372-1382.
• Slightly lower risk of prostate cancer, including advanced and aggressive cancers, among people treated with aspirin for 3 years or longer compared to less use in a meta-analysis of observational studies¹⁹¹Sauer CM, Myran DT et al. Effect of long term aspirin use on the incidence of prostate cancer: a systematic review and meta-analysis. Critical Reviews in Oncology/Hematology. 2018 Dec;132:66-75.
• Slightly lower risk of prostate cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 29 observational studies¹⁹²Wang X, Lin YW et al. Meta-analysis of nonsteroidal anti-inflammatory drug intake and prostate cancer risk. World Journal of Surgical Oncology. 2014 Oct 5;12:304.
• 14% lower risk of prostate cancer and 17% lower risk of advanced prostate cancer among people treated regularly with aspirin compared to less use, and stronger benefits from use for 4 years or more, in a meta-analysis of 24 observational studies¹⁹³Huang TB, Yan Yet al. Aspirin use and the risk of prostate cancer: a meta-analysis of 24 epidemiologic studies. International Journal of Urology and Nephrology. 2014 Sep;46(9):1715-28.
• Slightly lower risk of prostate cancer (23 studies), with stronger effects for advanced cancer (13 studies) but no evidence of an effect on non-advanced cancer (6 studies), among people treated with aspirin compared to no aspirin in meta-analyses of observational studies¹⁹⁴Liu Y, Chen JQ et al. Effect of aspirin and other non-steroidal anti-inflammatory drugs on prostate cancer incidence and mortality: a systematic review and meta-analysis. BMC Medicine. 2014 Mar 28;12:55.
• Slightly lower risk of prostate cancer among people treated with aspirin compared to no aspirin in a meta-analysis of 28 observational studies¹⁹⁵Qiao Y, Yang T et al. Associations between aspirin use and the risk of cancers: a meta-analysis of observational studies. BMC Cancer. 2018 Mar 13;18(1):288.
• 32% lower risk of lethal prostate cancer among healthy male physicians using aspirin regularly compared to never users in a very large RCT¹⁹⁶Downer MK, Allard CB et al. Regular aspirin use and the risk of lethal prostate cancer in the Physicians’ Health Study. European Urology. 2017 Nov;72(5):821-827.

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of thyroid cancer among people treated regularly with aspirin

• No evidence of an effect on risk of thyroid cancer among people treated regularly with aspirin compared to no aspirin in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 3 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁹⁷Patel D, Kitahara CM et al. Thyroid cancer and nonsteroidal anti-inflammatory drug use: a pooled analysis of patients older than 40 years of age. Thyroid. 2015 Dec;25(12):1355-62.

Aspirin and statins

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of substantially lower risk of gallbladder cancer among people treated with both aspirin and statins

• Substantially lower risk of gallbladder cancer among people treated with both aspirin and statins compared to neither in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁹⁸Prasai K, Tella SH et al. Aspirin and statin use and the risk of gallbladder cancer. Cancers (Basel). 2021 Mar 9;13(5):1186.

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of moderately lower risk of Barrett’s esophagus among people treated with both statins and aspirin

• Moderately lower risk of Barrett’s esophagus among people treated with both statins and aspirin compared to neither, and lower risk when both therapies are compared to statins alone, in a mid-sized observational study¹⁹⁹Beales IL, Dearman L, Vardi I, Loke Y. Reduced risk of Barrett’s esophagus in statin users: case-control study and meta-analysis. Digestive Diseases and Sciences. 2016 Jan;61(1):238-46.