Microbiome’s Impact on Cancer Treatment: Strategies for a Healthy Gut

Investigation of the human microbiome has grown exponentially in the last five years. A recent study regarding its potential impact on certain cancer treatment outcomes stopped me in my tracks.

The human body contains about 40 trillion microbes, which is now thought to equal the total volume of human cells each body possesses. These bugs offer helpful protection, or can act as insidious intruders wreaking havoc on our immune system, metabolism, and endocrine system.

It is widely acknowledged that 80% of our immune system resides in our gut. Therefore, healthy microbiota—bio-diverse gut flora comprised of healthy strains of bacteria—may offer a powerful key to preventing disease, including cancer.

Turns out, a healthy microbiome may also significantly enhance the treatment outcomes of anticancer agents, most notably novel targeted immunotherapies.

Microbiome and Anticancer Agents

Dr. Jennifer Wargo, melanoma expert and researcher, is a surgical oncologist at MD Anderson Cancer Center. Wargo became captivated when hearing a lecture presented by an investigator, from another institution, on a study showing how mice responded differently to certain cancer therapies, dependent on the biodiversity of the bacteria in their guts.

Immune checkpoint inhibitors have become popular immunotherapy agents, but are only effective 20-30% of the time. Wargo set out to discover if the microbiota in patients’ bodies helped determine how they responded to specific immunotherapy.

Her study involved metastatic melanoma patients. Initially, stool samples were collected. Patients were then infused with immunotherapy every three weeks. After several months, the patients underwent body scans to evaluate the state of their tumors. Subsequently, the patients were divided into two groups: responders (tumor stabilized, reduced in size, or disappeared) and non-responders (tumors grew, spread).

As in the mice study that preceded it, human responders had a much higher diversity of microbes than non-responders. Wargo’s team was also able to identify certain ‘beneficial’ bacteria associated with more positive responses to immunotherapy.

But association does not prove causation, so Wargo and company went back to the lab and infused the stomachs of melanoma-ridden mice with stool from the human responders. Even prior to introducing the immunotherapy, the tumors in these mice started growing more slowly; their immune system was rejecting the tumors. Mice who received non-responder human feces did not do nearly as well.

[See Glenn Sabin’s Anticancer Foods List]

Wargo’s preclinical animal study and small observational clinical study has gained wide attention in the field. To wit, her lab has teamed up with the Parker Institute for Cancer Immunotherapy, and Seres Therapeutics, to test the latter’s “oral microbiome therapy comprising a rationally-designed consortium of live bacteria, to improve the efficacy and safety of immunotherapy”.

[Related content: Penn Study Maps Potential of Manipulating Gut Microbiome to Boost Efficacy of Cancer Immunotherapies]

We may be a long way from securing empirical evidence that specific attributes of one’s gut flora improve immunotherapy or, for that matter, if they positively potentiate any anticancer agents, including chemotherapy.

Moreover, we have much to learn about the microbiome in general—the role it may play in cancer prevention or the onset of disease; how it may stimulate or inhibit tumor growth; or what role and impact it may play on cancer survivorship.

From Fringe to Center Stage

Gut health and the microbiome started out as an area of keen interest in the integrative and functional medicine community.

I recall the first lecture I heard in 2012, up on Copper Mountain in Colorado. An emergency medicine physician, Dr. Joe Alcock, delivered an amazing lecture on gut flora and its potential impact on human health.  He described a number of cases, including one about a woman who had an uncontrollable staph infection and was gravely ill. Only after getting a last-ditch effort experimental fecal transplant was she able to ward off the infection and resolve her acute situation.

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The audience was transfixed, if not just a little grossed out. Now it is commonplace to hear about fecal transplants for MRSA infections.

Gastrointestinal issues such as irritable bowel syndrome drive many patients to seek help from integrative and functional medicine providers. This typically happens after these patients run out of effective pharmaceuticals options prescribed by gastroenterologists. Today, testing the gut health of patients suffering from a variety of conditions is standard process.

We Don’t Know What We Don’t Know

We do not yet know every strain of bacterium that is most helpful or harmful to prevent or manage every condition; or to avoid cancer, complement active treatment, or to prevent relapse.

We don’t even know exactly how many microbes exist. Of those we are aware of, we generally know which strains are healthy and which are potentially harmful.

But here’s the thing: if we (1) know that 80+ percent of our immune system resides in the gut; and (2) can agree that anyone looking to avoid, treat, or prevent a recurrence of cancer would benefit from a super-charged immune function; then (3) we don’t need to wait for more scientific evidence to emerge before engaging in proactive, sensible and safe lifestyle behavior.

Are you with me? Let’s go…

 17 Ways to Supercharge Your Microbiome

  1. Eliminate sugar.
  2. Cut down on consumption of animal fat.
  3. Avoid processed foods of all kinds and, ideally, increase organically grown food following EWG’s recommendations.
  4. Increase your fiber intake.
  5. Expand the diversity of your diet, including fermented foods (probiotics) and prebiotics.
  6. Spend time in nature … get your hands (and feet) dirty.
  7. Think twice before taking antibiotics.
  8. Lower your stress load.
  9. Be aware of drugs that interact with the microbiome.
  10. Drink alcohol in moderation; preferably none at all.
  11. Stop smoking.
  12. Give antibacterial lotions a pass.
  13. Avoid using hand sanitizers.
  14. Get a good night’s
  15. Rescue a dog!
  16. Pick up bacteria from healthy partners and other people.
  17. Consider intermittent fasting (under medical supervision).

No One-Size-Fits-All Approach to Achieving Optimal Gut Health

It is my hope that you will be able to incorporate many of the recommendations in this list to immediately improve your gut flora. However, we are each different—with different challenges, needs, and limitations. Adding cancer to the equation makes it even more complex.

Perhaps you have problems digesting fermented foods. Or maybe intermittent fasting is not a good match for your overall health condition. Or possibly you are already suffering with underlying digestive issues, on active drug treatment for chronic IBS, or taking additional drugs that carry their own set of possible contraindications and side effects.

I emphasize these various challenging scenarios because we each have unique situations, and there is no one-size-fits-all solution to achieving healthy gut flora. For some, the most practical and smartest approach to a fine-tuned microbiome is to seek professional guidance.

Work with a Specialist with Expertise in Gut Health and Microbiome

If you have underlying digestive disorders, you should seek the support of a qualified integrative or functional medicine practitioner. Providers may also include nutritionists and dieticians trained and experienced in this area.

High quality, experienced clinicians and labs are available for testing your microbiome. While I endorse no particular tests, labs, probiotic dietary supplements, or practitioners, I do feature a directory of North American integrative oncology providers here, and a larger list of integrative and functional medicine providers here.


  • Valuable research continues apace on all things microbiome, including how it may affect drug therapy for cancer patients.
  • While more research is needed, we can each proactively strive to improve our gut health—therefore strengthen the immune system—by incorporating practical lifestyle recommendations (like those included in this article).
  • Consider working with a seasoned practitioner with the experience and expertise to support your self-directed lifestyle, with proper evaluation, testing, and, as needed, product recommendations such as probiotics.

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