Cancer is a disease that has perplexed, evaded, and devastated. The pharmaceutical industry has been desperately searching for a drug to satisfy the seemingly unattainable: a silver bullet for cancer. Cancer is not a singular entity but a diverse group of diseases with complex genetic, molecular, and environmental underpinnings. This complexity necessitated a shift from seeking a singular “magic bullet” cure to developing a multi-faceted approach.
Considering the heavy resource burden of clinical drug development, researchers are increasingly interested in discovering if already approved drugs may have some use in the complex case of cancer. With a little over 1,000 approved cancer drugs listed in the United States and Europe,1Pantziarka P, Capistrano RI, De Potter A, Vandeborne L, Bouche G. An Open Access Database of Licensed Cancer Drugs. Frontiers in Pharmacology. 2021 Mar 11:12:627574. there is no shortage of different pharmaceutical options to treat cancer. People refer to the use of drugs for purposes other than their FDA-approved indications as off-label use. The term for these drugs now gaining favor is “repurposed drugs.”
With widespread access to cancer research studies and anecdotal stories through Internet searches and social media, people with cancer are becoming increasingly proactive in exploring all available treatment options. This trend has spurred grassroots adoption of complex supplement regimens and repurposed drug protocols. The fact that there is some evidence for various repurposed drugs to improve cancer outcomes makes it tempting for individuals to assume these drugs will help their cancer. When facing a dire cancer diagnosis and presented with a potential option, the hope for success may overshadow the specifics of the evidence.
As providers of an evidence-based cancer resource for people with cancer seeking a whole-person approach to care, we aimed to gather insights from research, clinicians, and patients to shed light on these developments.
A brief history of repurposed drugs in cancer care
In the quest to develop effective cancer treatments, drug repurposing is nothing new. Researchers first discovered the first chemotherapeutics accidentally while experimenting with mustard gas, observing that it decreased tumor size.2Adair FE, Bagg HJ. Experimental and clinical studies on the treatment of cancer by Dichlorethylsulphide (Mustard Gas). Annals of Surgery. 1931;93:190–9. In 1972, researchers observed in mice that aspirin prevents metastases, providing the first preclinical evidence of its potential as a cancer treatment.3Gasic GJ, Gasic TB, Murphy S. Anti-metastatic effect of aspirin. Lancet. 1972 Oct 28;2(7783):932-3; Gasic GJ, Gasic TB, Stewart CC. Antimetastatic effects associated with platelet reduction. Proceedings of the National Academy of Sciences of the USA. 1968 Sep;61(1):46–52. It wasn’t until years later that clinical studies would investigate this further, and the evidence would demonstrate that aspirin did indeed have a role in reducing cancer risk, and also in decreasing metastases.4Rothwell PM, Wilson M, Price JF, Belch JF, Meade TW, Mehta Z. 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; Langley RE, Burdett S et al. Aspirin and cancer: has aspirin been overlooked as an adjuvant therapy? British Journal of Cancer. 2011 Aug 16;105(8):1107–1113.
A recent study on cancer treatments reported that doctors gave 18.6% of patients an “off-label” cancer drug, meaning a drug approved for a different cancer than the one diagnosed.5National Cancer Institute. Off-label drug use in cancer treatment. Jan 13, 2022. An example is oxaliplatin, approved for colorectal cancer, and used in triple-negative breast cancer patients even though it isn’t “on-label.”6Liu R, Wang R et al. Systematic analysis of off-label and off-guideline cancer therapy usage in a real-world cohort of 165,912 US patients. Cell Reports Medicine. 2024 Mar 19;5(3):101444.
Online cancer forums and health information
Limited attention from doctors and short visit times are not news. Overburdened healthcare institutions and doctors leave patients frustrated. Amplified fear in people with cancer leads them to seek out any option available to them. Yet few people diagnosed with cancer have the training to discern which treatments are safe and effective. It takes time to learn how to understand scientific research and discern quality evidence.
Outside of counsel with a doctor, Americans mainly find their health information via Internet sources like social media, health websites, or online news platforms.7Hannon, C. Health Information: What Sources Do People Trust? PatientsLikeMe Blog. Retrieved November 26, 2024. An estimated 67% of cancer information shared on social media is scientifically accurate, which highlights that there are many sources that are not.8Gage-Bouchard EA, LaValley S, Warunek M, Beaupin LK, Mollica M. Is Cancer Information Exchanged on Social Media Scientifically Accurate? Journal of Cancer Education. 2018 Dec;33(6):1328-1332. Online forums, like Reddit and Facebook groups, are becoming major hubs for sharing DIY cancer treatment protocols. While these provide important community support connections, cancer therapy recommendations are often anecdotal.
Jane McLelland published How to Starve Cancer in 2018, describing how she sought to eradicate her terminal cancer. She developed her protocol by identifying specific cancer pathways as targets, then looking for existing drugs and supplements that might act on those pathways. She created a cocktail of supplements, and repurposed drugs like metformin, to attack specific cancer pathways, while incorporating lifestyle practices such as exercise and diet, and conventional cancer treatments. Her story is powerful, and her strategy scientific. The book does not offer a specific protocol, and researchers have not tested any of her approaches in animals or humans to demonstrate efficacy. Her systematic approach stimulated discussion in the medical community, and for people with cancer.
Will LaValley, a medical doctor and Molecular Integrative Oncology physician consultant, shares the scientific rationale behind this approach. He explains that cancer relies on complex networks of molecules to develop, grow and spread. It is necessary to use a molecular network biology approach to manage the cancer that evolves from early to advanced stages. This approach uses cell and animal studies to figure out multiple molecular network targets. Then repurposed off-label drugs and natural products that target multiple molecular networks are selected to provide an additive and synergistic effect to conventional treatment. In his book Beyond the Magic Bullet, Raymond Chang, MD, calls this a “cocktailed” approach.
There are over 100,000 members in Jane McLelland’s “Off Label Drugs” Facebook group at the time of this article. Her methods resonate with people who have cancer as they seek options beyond conventional care from their oncologists. The publication of her book has contributed to the rise in popularity of repurposed drugs, alongside the widespread engagement with social platforms for health information. This has sparked a fervor online with people searching for peers sharing success with repurposed drugs. Anecdotal success stories shared in forums sometimes neglect to mention the conventional therapies taken in addition to off-label drugs.
The growing popularity of fenbendazole, a dog dewormer, illustrates how patient anecdotes can drive interest in repurposed drugs for cancer treatment. One patient’s reported success in using fenbendazole has led to its widespread attention among cancer patients. This has fueled the growth of fenbendazole-focused Facebook groups, one of which now boasts over 100,000 followers. Within these communities, patients share personal stories, successes, and challenges with incorporating the drug into their cancer treatment protocols, reflecting a grassroots approach to exploring unconventional, often unproven therapies.
On January 9th, 2025, Actor Mel Gibson shared on Joe Rogan’s podcast that he has three friends who had stage 4 cancer and “all three of them don’t have cancer right now at all” followed by “they took some of what you’ve heard they’ve taken, ivermectin, fenbendazole” implying the two drugs healed his friend’s cancer. These comments have sparked a significant increase in interest in fenbendazole, as reflected in the surge in traffic to CancerChoices’ review of the drug.
Is there clinical evidence?
Alongside amplified interest, there are early stage clinical trials looking specifically at drugs like hydroxychloroquine, and mebendazole for gliomas, and ivermectin and specific cancers.
Limited clinical (human) studies specifically look at improving cancer outcomes using popular repurposed drugs (metformin, statins, mebendazole) as an intervention. While there is plenty of clinical data on these drugs for their primary use, for example using metformin as a drug to control blood sugar levels for people with diabetes, clinical data on the drug’s effects on cancer are much more limited. Research findings on cancer may also be more difficult to interpret.
The CancerChoices review of metformin describes how hundreds of clinical studies have found improved cancer outcomes and decreased cancer risk associated with metformin use, but almost exclusively among people with diabetes. Across most studies of non-diabetic people, metformin has not improved cancer outcomes. These results are something to pay attention to, especially for clinicians, but it can be challenging for individuals to discern how metformin, or any other repurposed drug, might be useful in their case by reading isolated studies without knowing the full context and looking for broad patterns.
There are organizations looking to increase the evidence base to investigate if there truly are benefits for specific repurposed drugs as a cancer treatment. The Repurposing Drugs in Oncology (reDO) Project, an initiative of the Anticancer Fund in Belgium, compiled a database of the literature available on 372 licensed drugs of interest for cancer, currently not approved for use with cancer.
Pan Pantziarka, the Program Director of Drug Repurposing at the Anticancer Fund, shares the difficulty in researching repurposed drugs for cancer:
“The biggest challenge remains generating strong evidence of efficacy – this means running well-designed clinical trials that can show that a repurposed drug is effective as a cancer treatment. A lot of the evidence we have is pre-clinicalAny research about a treatment for a disease that occurs before it is tested by human volunteers. This research may be done on cells (in vitro) or in animals (in vivo). or isolated cases – we need more than that to be sure that a repurposed drug really does make a difference to outcomes. It’s a major challenge because trials are expensive, not always well-designed and frequently struggle to recruit patients, especially if there’s a competing trial with a lot of financial sponsorship and a fancy new drug rather than an old medicine used in a new way.”
“Dosage amount, frequency, duration and repetition of dosage cycles are ripe for clinical trials and I know of none being funded,” said Dr. Will LaValley who collaborates with patients’ integrative medicine physicians and oncologists to use repurposed drugs for their interested patients and clients.
Pantzlarka additionally highlights the economic challenges of repurposed drugs. Their cost-effectiveness can be both a benefit and a barrier. While their affordability makes them accessible, the lack of profit potential often discourages investment in further studies and clinical trials.
Often, without plentiful research in humans, researchers study the drug in the lab to figure out how a drug works, its “mechanism of action.” This helps set up a rationale for researching a repurposed use of a drug. “The potential clinical value of the benzimidazoles, mebendazole and fenbendazole, through anti-microtubule molecular mechanism is a rational repurposing of the drugs,” said LaValley explaining the scientific rationale for using mebendazole and fenbendazole for cancer since they target a mechanism other cancer drugs target.
CancerChoices reviewed the clinical research for mebendazole and fenbendazole. Fenbendazole is a veterinary medicine, so there are no studies in humans. Despite its promising mechanism of action, researchers propose that due to its poor solubility, orally administered fenbendazole may not reach sufficient systemic levels to impact tumors.9Nguyen J, Nguyen TQ, Han B, Hoang BX. Oral Fenbendazole for Cancer Therapy in Humans and Animals. Anticancer Research. 2024 Sep;44(9):3725-3735. We also discuss this specific drug in a separate blog post.
Research on mebendazole has mixed results: while three individual case studies reported improved quality of life in advanced cancer patients with limited options, controlled clinical trials found minimal benefits for brain tumor patients and weak improvements in colorectal cancer outcomes. More robust studies are needed to make strong recommendations for the use of mebendazole as a cancer treatment.
“For example, in some cancers which are treated with very intense and toxic chemotherapy, adding in a repurposed drug, even one that is known to be very safe, may be challenging. We can’t ignore existing treatments and start with a blank slate. Very few repurposed drugs are likely to be effective as mono-therapy, so we have to look at how we can schedule repurposed drugs into existing treatment protocols,“ said Pantziarka.
What do clinicians think?
Widespread patient interest compels clinicians to understand the benefits and risks of popular repurposed drugs. We asked trusted CancerChoices advisors about their perspectives on using repurposed drugs for cancer.
“I have had a dozen or so patients who used ivermectin before, most of them were stage 4. I have not seen any miraculous benefit from it. The several patients whose tumors actually responded were also getting conventional chemotherapy concurrently, so it wasn’t really surprising to me that their cancer improved,” said Dr. Walter Tsang, an oncologist.
Dr. Nina Fuller-Shavel, an Oxbridge-trained physician specializing in integrative cancer care, stressed the importance of determining a patient’s suitability for a specific drug and that a “one size fits all” approach is inappropriate. “When considering repurposed drugs, it’s important to conduct a personalized assessment using patient biomarkers and clinical history and to look for interactions with any current treatments or medical conditions, as well as the overall safety profile and broader physiological impact. Decisions are based on the full clinical picture, as well as understanding whether there is evidence for benefit from that particular drug, because there is much hearsay without back up. One must go and look deeply into the data to assess individual risk-benefit and discuss it properly with the patient within a shared decision-making conversation.”
Jen Green, a naturopathic oncologist, expressed her concern over patients taking various repurposed drugs without practitioner oversight. “The dose that patients plan to take or are taking varies so widely that it does concern me and I have no way to provide proper guidance on dose because we haven’t seen research results yet. I test liver enzymes in patients taking mebendazole or fenbendazole because I have once seen elevated liver enzymes that were coming from a woman taking fenbendazole.”
Dr. Tsang observed liver toxicity in his patients as well. “I have seen several cases of liver toxicity from it. The most serious one just occurred recently. Someone was taking fenbendazole, ended up overdosing on it and developed liver failure that required hospitalization.”
“I think we need to get very smart when we think about repurposed drugs. Is it the right drug for the right patient, at the right dose for the right duration and at the right time? How is it monitored and are any side effects and potential toxicities considered? And how do you know if it’s been effective?” said Dr. Fuller-Shaval.
The patient perspective
Lindsay McDonell, a metastatic breast cancer survivor and cancer coach, shared her experience with repurposed drugs. “I pursued repurposed drugs for a very short time. I stopped because I did not feel I was being supervised in a way I felt comfortable. I needed more supervision. I tried to understand the most popular books on the subject. I believe that one would need very close monitoring and also a true understanding of any mutations they might have before they go down this path. They have worked for some but I was not at all convinced it was safe for me. With what I know now about my own body, blood, progression etc. I am glad it was a very short time that I tried them.”
She additionally reflected on the forums popular with so many cancer patients, “I do not believe the forums offer enough to send someone to forgo conventional or integrative treatment without deep, deep knowledge of their own situation and the majority of patients simply do not have that.”
The future of repurposed drugs in cancer care
Further study is needed to determine if targeting specific cancer pathways could meaningfully impact cancer outcomes, particularly with the use of affordable, existing drugs. Research would provide greater insight on how to use drugs like metformin and mebendazole safely and effectively as complementary cancer therapies. However, the current evidence base does not provide clear guidance to patients or clinicians, and clinicians are observing potentially harmful side effects in patients taking repurposed drugs.
Rigorous clinical trials are essential to validate the safety and efficacy of repurposed drugs in specific cancer contexts. It is crucial to ensure that patients have access to trustworthy, evidence-based information. Patients must approach repurposed drug strategies with a clear understanding of the risks and benefits, ideally under the guidance of qualified healthcare professionals.
References
Christine has a dynamic background in the life sciences, public health, and program operations. Her career began at the lab bench with a Gates Foundation-funded HIV Vaccine research group, which led her to graduate studies in public health epidemiology at UC Berkeley. Her research experience spans clinical epidemiology research to evaluating the impacts of community nutrition programs in Los Angeles, the Central Valley, and Oakland. Most recently she has worked in executive operations for a seed-stage venture capital firm based in San Francisco. Personally, Christine is passionate about holistic health and wellness. She is a clinical herbalist and Reiki master, and she has been practicing yoga for 15+ years. She brings a breadth of experiences to her work leading the CancerChoices program.
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