The future of treating cancer might just include a dose of donated poop. A pair of small trials out this week have found that fecal microbiota transplantation (FMT)—thankfully delivered via a pill—can potentially give other cancer treatments a much-needed boost.

Scientists in Canada conducted the two trials, both published Wednesday in Nature Medicine. In one trial of people with advanced kidney cancer, FMT appeared to reduce the side effects of immunotherapy; in the other, it reportedly improved the actual outcomes of people with lung cancer or melanoma given immunotherapy. The findings suggest FMT can be a promising add-on to an already valuable approach for treating late-stage cancers, the researchers say. The international study included scientists from Italy, the United States, and France.

Poop in pill form

The gut microbiome—the community of bacteria that live along our digestive tract—plays an important part in our health. And numerous conditions have been linked to a dysfunctional microbiome. FMT rebuilds a person’s microbiome by using someone else’s healthy gut bacteria as the template.

FMT is highly effective at treating recurrent C. difficile infections. Unfortunately, it’s proven harder to find other consistent applications for it. Another limiting factor for some people is that the treatment typically has to be provided through a colonoscopy or enema. But scientists at the Lawson Research Institute, part of St. Joseph’s Health Care London in Ontario, have been working to develop customized FMT pills that can be taken orally instead. Both trials used these pills.

In a Phase I trial led by researchers at Lawson and London Health Sciences Centre Research Institute (LHSCRI), FMT was given to 20 patients with metastatic renal cell carcinoma. The patients had all taken immunotherapy drugs, treatments that boost the immune system’s natural defenses against cancer, prior to their FMT.

Compared to standard treatment, the participants reported fewer side effects associated with immunotherapy, such as rash, nausea, and diarrhea. About 50% of people also showed a treatment response. That’s higher than the typical rate for these medications, though the study was not primarily intended to evaluate effectiveness.

Researchers at the Montreal University Hospital Center’s research center conducted the second, Phase II, study. People with advanced lung cancer or melanoma given both FMT and immunotherapy experienced a response rate of 75% to 80%—well above the typical 39% to 45% rate seen with these treatments, the researchers say.

Early but promising

Those studies are still small in size, so their findings should be viewed with some caution. But they certainly make the case for larger, more extensive trials to further test out FMT as a boon to cancer treatment, and some trials are already underway.

“To use FMT to reduce drug toxicity and improve patients’ quality of life while possibly enhancing their clinical response to cancer treatment is tremendous, and it had never been done in treating kidney cancer before this,” said Michael Silverman, an author in both studies and head of the infectious diseases program at St. Joseph’s Health Care London in Ontario, in a statement from the LHSCRI.

Even in pill form, donated poop might be a hard treatment for some people to stomach. But it could very well help save the lives of people who otherwise wouldn’t have responded to standard care someday soon.