Your Microbiome

Over thousands of years, our bodies have developed a symbiotic relationship with organisms living in and on our bodies, generally supporting each other’s health and well-being. Research links your microbiome—and changes in it—to several types of cancer and how well you respond to some conventional cancer treatments.

Why is your microbiome important?

Links have been found between the composition of your microbiome—your particular collection of microbes—and cancer outcomes. Your micriobiome also affects other body terrain factors and side effects common in cancer.

Connections to cancer outcomes

Researchers are finding that some microorganisms may have a direct connection to development or proliferation of cancer, as shown so far in a few cancer types.

Colorectal 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 a link between the microbiome and cancer; we don’t know if changes in the microbiome contribute to cancer, or if cancer contributes to changes in the microbiome, or if the link works in both directions

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 higher risk of colon cancer but lower risk of rectal cancer, mostly among women, among people with the highest use of antibiotics

Gastrointestinal cancer

Esophageal cancer: 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 a link between esophageal cancer and an altered gut microbiome; we don’t know if changes in the microbiome contribute to cancer, or if cancer contributes to changes in the microbiome, or if the link works in both directions

Gallbladder cancer: preliminary evidence of a link between chronic bacterial infection of bile and gallbladder cancer; we don’t know if the infection contributes to cancer, or if cancer contributes to infection, or if the link works in both directions

Stomach cancer: preliminary evidence of a link between stomach cancer and an altered gut microbiome; we don’t know if changes in the microbiome contribute to cancer, or if cancer contributes to changes in the microbiome, or if the link works in both directions

Gynecological cancer

Good evidence of a link between human papillomavirus and cervical cancer

Head, neck, and oral cancer

Preliminary evidence of a link between the larynx and throat microbiome and laryngeal carcinoma; we don’t know if changes in the microbiome contribute to cancer, or if cancer contributes to changes in the microbiome, or if the link works in both directions

Lung cancer

Preliminary evidence of more advanced cancer among people with certain microorganisms that are normally found in the mouth present within the lungs

Preliminary evidence of better survival among people with lung cancer with more microbe compositional diversity

For both these findings, we don’t know if changes in the microbiome contribute to cancer progression, or if cancer progression contributes to changes in the microbiome, or if the link works in both directions.

Ovarian cancer

Preliminary evidence of higher incidence of ovarian cancer or BRCA1 mutation status among women with lower levels of the protective bacteria Lactobacillus in the microbiota in the cervix; we don’t know if changes in the microbiome contribute to cancer, or if cancer contributes to changes in the microbiome, or if the link works in both directions

Pancreatic cancer

Preliminary evidence of altered oral microbes among people with pancreatic cancer

Preliminary evidence of a substantially different pancreatic microbiome among people with pancreatic cancer

For both these findings, we don’t know if changes in the microbiome contribute to cancer, or if cancer contributes to changes in the microbiome, or if the link works in both directions.

Connections to conventional cancer treatments

The composition of your microbiome can influence how well you respond to chemotherapy, immunotherapy, or stem cell transplant. Your gut microbiota is particularly influential in these situations:26Peled JU, Gomes ALC et al. Microbiota as predictor of mortality in allogeneic hematopoietic-cell transplantation. New England Journal of Medicine. 2020;382(9):822–834; Block KI, Block PB, Gyllenhaal C. Integrative treatment for colorectal cancer: a comprehensive approach. Journal of Alternative and Complementary Medicine. 2018;24(9-10):890–901; Bultman SJ. Emerging roles of the microbiome in cancer. Carcinogenesis. 2014;35(2):249–255; Gopalakrishnan V, Helmink BA, Spencer CN, Reuben A, Wargo JA. The influence of the gut microbiome on cancer, immunity, and cancer immunotherapy. Cancer Cell. 2018;33(4):570‐580; Routy B, Le Chatelier E et al. Gut microbiome influences efficacy of PD-1-based immunotherapy against epithelial tumors. Science. 2018 Jan 5;359(6371):91-97; Stein-Thoeringer CK, Saini NY et al. A non-antibiotic-disrupted gut microbiome is associated with clinical responses to CD19-CAR-T cell cancer immunotherapy. Nature Medicine. 2023 Mar 13.

  • A healthy gut microbiome appears to support the anticancer action of the chemotherapy drug oxaliplatin.
  • Your gut microbiota can shape your response to platinum-based chemotherapies and cyclophosphamide therapy.
  • Your gut microbiome is a main player in your response and toxicity to immunotherapy treatments, including immune checkpoint blockade and CAR-T therapy. For instance, bacteria in the genus Bifidobacterium are crucial to optimizing the anticancer action of ligand 1 drugs (PD 1 checkpoint inhibitors), which activate your immune system to attack tumors.
  • The condition of the gut microbiota is associated with differences in long-term survival following allogeneic stem cell transplant › (transplant of cells from a matching donor) and in the toxicity of graft versus host disease (GvHD) › which might follow an allogeneic stem cell transplant.
  • Gut microbes can prevent reactivation of chemotherapy metabolites in your intestines—such as camptothecin metabolites—that can damage your intestines and cause diarrhea.

The composition of the microbiome may influence responses to immunotherapy. Studies have investigated manipulating the gut microbiome to enhance responses to cancer immunotherapy.27Gopalakrishnan V, Helmink BA, Spencer CN, Reuben A, Wargo JA. The influence of the gut microbiome on cancer, immunity, and cancer immunotherapy. Cancer Cell. 2018;33(4):570‐580.

Connections to body terrain factors

Your microbiome has links to several other body terrainthe internal conditions of your body, including nutritional status, fitness, blood sugar balance, hormone balance, inflammation and more factors. Sometimes the cause and effect are seen in both directions (bidirectional). Sometimes an imbalance in one terrain factor causes a domino effect, toppling the balance of other terrain factors. Details of these connections follow, but first we want to emphasize the web of connections among factors that aren’t as apparent by looking at factors one at a time.

Your microbiome influences and is influenced by glucose. Because of its important metabolic function, your microbiome may influence the development of both obesity and diabetes. An imbalanced gut microbiota is linked to impaired blood sugar control, insulin resistance and development of type 2 diabetes.34Gérard C, Vidal H. Impact of gut microbiota on host glycemic control. Frontiers in Endocrinology (Lausanne). 2019 Jan 30;10:29. People with impaired blood sugar control have lower levels of helpful gut bacteria. Though we find worse microbial imbalance in people with excess body weight, weight loss tends to improve microbial balance. Measures to improve the health of your microbiome, such as through a high-fiber, plant-based diet, may promote beneficial microorganisms and contribute to the health of your metabolism. 

Your microbiome has a hand in hormone balance, specifically estrogen metabolism. Some microbes in the intestine are estrogenic and others anti-estrogenic, which may ultimately have some influence in cancers driven by estrogen.   

Your microbiome, when in balance, can be a champion for healthy immunity. For instance, healthy microorganisms can keep disease-causing (pathogenic) microorganisms in check. A balanced microbiome can also stimulate the development of T- helper cells, which fight infection. A healthy microbiome can inhibit immune factors that promote chronic inflammation.    

Bottom line: Your microbiome is connected with many other terrain factors. We recommend you work with your healthcare practitioner to determine which terrain imbalances you may have and what is driving those imbalances. Then you can make a plan to optimize your terrain in the most sensible way. For instance, if you struggle to manage excess body weight, you may want a healthy weight-loss program that includes foods that help restore and maintain your microbiome balance from your mouth to your colon.    

Body weight

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 worse microbial balance among people who are obese and of improved balance among people losing weight

High blood sugar and insulin resistance

Modest evidence of a link between insulin sensitivity/diabetes and gut microbial composition and diversity; we don’t know which direction the link operates, or if it operates in both directions

Hormone imbalance

Research has found links between estrogen levels and your microbiome; we don’t know which direction the links operate, or if they operate in both directions.

Immune function

Your immune system and microbiota are linked; disturbances to their balance can create or contribute to inflammation. We don’t know which direction the link operates, or if it operates in both directions.

Inflammation

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 more pronounced inflammatory symptoms among people with low bacterial richness (number of gut microbial genes); we don’t know which direction the link operates, or if it operates in both directions

Connections to symptoms and side effects of cancer

Anxiety

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 a link between anxiety or fear of cancer recurrence and the composition of the gut microbiome among people with breast cancer; we don’t know which direction the link operates, or if it operates in both directions

Cardiovascular symptoms

Preliminary evidence of a link between cardiorespiratory fitness among people with breast cancer and changes in frequency of certain gut bacteria genera; we don’t know which direction the link operates, or if it operates in both directions

Fatigue

Preliminary evidence of more fatigue among people with breast cancer with changes in frequency of certain gut bacteria genera

Gastrointestinal symptoms

Preliminary evidence of a link between microbial diversity and diarrhea; we don’t know which direction the link operates, or if it operates in both directions

Neurological symptoms

Preliminary evidence of a higher risk of psychoneurological symptoms among people with head and neck cancer with a greater change in microbes after radiation therapy; we don’t know which direction the link operates, or if it operates in both directions

Quality of life and physical function

Preliminary evidence of worse quality of life scores among people with breast cancer with higher levels of Ruminococcus or Dorea microbes; we don’t know which direction the link operates, or if it operates in both directions

Sleep disruption

Preliminary evidence of more sleep dysfunction among people with breast cancer with changes in frequency of certain gut bacteria genera; we don’t know which direction the link operates, or if it operates in both directions

Symptoms not specific to cancer

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 link between the large intestine microbiome and changes in several factors related to appetite and obesity; we don’t know which direction the link operates, or if it operates in both directions

Preliminary evidence of a link between microbiome composition and depression; we don’t know which direction the link operates, or if it operates in both directions

CancerChoices advisor Brian Bouch, MD, explains the importance of the microbiome in integrative cancer care.

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Helpful links

With gratitude to Julie M. Deleemans, MSc, PhD(c), for her contributions

Journal articles

Shreiner AB, Kao JY, Young VB. The gut microbiome in health and in disease. Current Opinion in Gastroenterology. 2015 Jan;31(1):69-75.

Francescone R, Hou V, Grivennikov SI. Microbiome, inflammation, and cancer. Cancer Journal. 2014 May-Jun;20(3):181-9.

Authors

Laura Pole, RN, MSN, OCNS

Senior Clinical Consultant
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Laura Pole is senior clinical consultant for CancerChoices. Laura is an oncology clinical nurse specialist who has been providing integrative oncology clinical care, navigation, consultation, and education services for over 40 years. She is the co-creator and co-coordinator of the Integrative Oncology Navigation Training at Smith Center for Healing and the Arts in Washington, DC. Laura also manages the “Media Watch Cancer News That You Can Use” listserv for Smith Center/Commonweal. In her role as a palliative care educator and consultant, Laura has served as statewide Respecting Choices Faculty for the Virginia POST (Physician Orders for Scope of Treatment) Collaborative as well as provided statewide professional education on palliative and end-of-life care for the Virginia Association for Hospices and Palliative Care.

For CancerChoices, Laura curates content and research, networks with clinical and organizational partners, brings awareness and education of integrative oncology at professional and patient conferences and programs, and translates research into information relevant to the patient experience as well as clinical practice.

Laura sees her work with CancerChoices as a perfect alignment of all her passions, knowledge and skills in integrative oncology care. She is honored to serve you.

Laura Pole, RN, MSN, OCNS Senior Clinical Consultant

Nancy Hepp, MS

Lead Researcher
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Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher and writer for CancerChoices and also served as the first program manager. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.

Nancy Hepp, MS Lead Researcher

Andrew Jackson, ND

Research Associate
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Andrew Jackson, ND, serves as a CancerChoices research associate. As a naturopathic physician practicing in Kirkland, Washington, he teaches critical evaluation of the medical literture at Bastyr University in Kenmore, Washington. His great appreciation of scientific inquiry and the scientific process has led him to view research with a critical eye.

Andrew Jackson, ND Research Associate

Last update: April 9, 2024

Last full literature review: July 2021

CancerChoices provides information about integrativein cancer care, a patient-centered approach combining the best of conventional care, self care, and evidence-informed complementary care in an integrated plan cancer care. We review complementaryin cancer care, complementary care involves the use of therapies intended to enhance or add to standard conventional treatments; examples include supplements, mind-body approaches such as yoga or psychosocialtherapy, and acupuncture therapies and self carelifestyle actions and behaviors that may impact cancer outcomes; examples include eating health-promoting foods, limiting alcohol, increasing physical activity, and managing stress practices to help patients and professionals explore and integrate the best combination of conventionalthe cancer care offered by conventionally trained physicians and most hospitals; examples are chemotherapy, surgery, and radiotherapy and complementary therapies and practices for each person.

Our staff have no financial conflicts of interest to declare. We receive no funds from any manufacturers or retailers gaining financial profit by promoting or discouraging therapies mentioned on this site.

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