New research shows just how important our intestinal bacteria are for our health. The kind of bacteria in our intestines can actually play a big role in how patients with cancer respond to their treatment.

Microbes inhabit just about every part of the human body outnumbering human cells by ten to one. Darryl Leja, NHGRI. Credit: The U.S. National Institutes of Health

The researchers examined patients with advanced melanoma and how their respective gut bacterial flora – microbiome – might influence how well the patients respond to cancer treatment.

“We got strong evidence that the intestinal flora largely shapes how patients respond to treatment,”

– Jennifer Wargo, M.D. at the University of Texas and one of the researchers involved in the study published in Science.

A more common form of cancer treatment is immunotherapy, by which the immune system is activated to fight cancer tumors. But researchers have long wondered why a large number of patients are non-responders to this type of treatment. A possible answer is that some patients miss several of the bacteria that are good for the intestines.

By mapping which bacteria were present in the patient’s intestinal tract, researchers at The University of Texas could see that those who responded best to immunotherapy treatment were those who had a varied intestinal flora and a large amount of, particularly good bacteria.

“The difference in the intestinal flora between those who became healthier and those who became sicker was like night and day,”

– Jennifer Wargo.

For the next phase, the researchers transplanted samples from patients to mice, to check if the intestinal bacteria was indeed the cause of the apparent correlation between specific bacteria and cancer treatment prognoses.

The mice with tumor cells did indeed cope better with bowel bacteria from patients who responded best to cancer treatments, compared to mice with bacteria from patients who were not responding well to cancer treatment.

Immune profiling suggested enhanced systemic and anti-tumor immunity in responding patients with a favorable gut microbiome, as well as in germ-free mice receiving fecal transplants from responding patients.

– The researchers conclude.

Much research in recent time has shown just how important the intestinal bacteria is for our health and general well being. Future research will possibly determine the exact mechanisms that cause the favorable effects.

“We still do not know what mechanisms are that make these bacteria good for treatment, but it raises interesting questions. It may be time to try to affect the intestinal flora of our cancer patients, “

– Jennifer Wargo.

The microbiome might help predict which melanoma patients that respond immunotherapy and in the near future, it might be relevant to transplant intestinal bacteria between patients who lack those bacteria deemed beneficial during cancer treatments.


J. A. Wargo, V. Gopalakrishnan, C. N. Spencer et al. Gut microbiome modulates response to anti–PD-1 immunotherapy in melanoma patients DOI: 10.1126/science.aan4236