One person’s waste could be another’s shot at fighting cancer.
The idea may sound far-fetched, but it is gaining momentum in cancer care.
Researchers are testing faecal microbiota transplants as a way of changing the gut’s microbes.
This could help treatments, such as immunotherapy, work better, and it could be especially significant for hard-to-reach cancers.
These faecal microbiota could also help deliver longer-lasting benefits for more patients.
Donor stools
As the name suggests, a faecal microbiota transplant introduces gut microbes from a carefully screened healthy donor’s stool into a patient’s gastrointestinal tract.
It is most often delivered through a colonoscopy procedure, though it can also be given through a tube passed through the nose into the stomach.
More recently, some transplants have been delivered in swallowable capsules.
The idea of stool as medicine is not new.
Records from fourth-century China describe “yellow soup,” a faecal mixture used to treat severe diarrhoea and food poisoning, that was reportedly considered a “medical cure,” according to a 2012 letter to the editor published in The American Journal Of Gastroenterology.
A modern precursor entered Western medicine in 1958, when doctors used faecal enemas to successfully treat four patients with pseudomembranous colitis, a severe intestinal inflammation often linked to a bacterium called clostridium difficile (C. diff).
Today, scientists have a clearer picture of how and why faecal microbiota transplants work.
“Over the last 20 years, people began to understand the gut microbiome seems to be involved in so many different things, the two major ones are your immune system and metabolism,” said Dr Andrew Koh, a paediatric haematologist-oncologist at UT Southwestern Medical Center in Dallas, Texas, United States, who studies the gut microbiome.
Gut microbes help train the immune system to recognise and respond quickly to real threats, such as pathogens or cancerous cells, Dr Koh said.
At the same time, they help keep that response in check, reducing the risk the immune system overreacts to harmless microbes or the body’s own tissues in ways that can fuel autoimmune diseases.
Boosting immunotherapy response
Since a landmark 2013 study showed faecal microbiota transplants were highly effective for patients with recurrent C. diff infections, the Food and Drug Administration has since approved the treatment for that use.
The bacterial infection causes nearly half a million illnesses in the US and an estimated 29,300 deaths each year, according to the Centers for Disease Control and Prevention.
In cancer care, faecal microbiota transplants are being used to treat some patients who develop gastrointestinal side effects from immunotherapy, said Dr Jennifer Wargo, a surgical oncologist at the University of Texas MD Anderson Cancer Center.
But researchers, like Dr Wargo, are studying whether the procedure can boost the effectiveness of immunotherapies, which help the body’s immune system find and kill cancer cells.
Over the past several years, studies have suggested some people with cancer have less diverse, less balanced communities of gut microbes, Dr Wargo said.
This disruption, often called dysbiosis, can happen for many reasons, including diet, antibiotic use and even physical activity levels.
But research so far suggests restoring the microbiome through a faecal microbiota transplant may improve how well some patients respond to immunotherapy and, in turn, their longer-term outcomes.
In a 2021 study, Dr Wargo and her colleagues performed faecal microbiota transplants in 10 people with advanced melanoma whose cancers had stopped responding to immunotherapy.
Three patients responded: Two had partial responses, meaning their tumours shrank, and one had a complete response, with no detectable cancer after treatment.
More recently, a Canadian study reported that giving faecal microbiota transplants before patients started immunotherapy for lung cancer or melanoma was linked to higher response rates.
In that trial, 75% of patients with melanoma who received a transplant responded to treatment, compared with the roughly 50% to 58% response rates typically seen with immunotherapy alone.
Getting involved
Faecal microbiota transplants are being studied at a time when cancer remains widespread in the US.
More than 148,000 new cancer cases were expected to be diagnosed in 2025 in Texas, including over 72,000 cancers in women and more than 76,000 cancers in men, according to the Texas Department of State Health Services.
For patients interested in faecal microbiota transplants, Dr Koh and Dr Wargo recommend talking to your oncologist.
Additionally, you can search Clinicaltrials.gov to see which studies are recruiting patients.
There are risks to transplanting another person’s stool, including a small but real chance of transferring harmful pathogens.
Dr Wargo cautioned against attempting a do-it-yourself transplant.
“With cancer patients, we’re concerned about safety,” she said.
“We don’t want people to be doing their own poop transplant.
“They need to work with their treatment teams, first and foremost.” – The Dallas Morning News/Tribune News Service
