New research from the University of California, San Francisco (UCSF) has found that certain bacteria living in the human gut may help protect cancer patients from the harsh side effects of chemotherapy.
These findings suggest that the microbes in our digestive systems could play an important role in how patients respond to treatment—and even open up the possibility of using probiotics to improve cancer care.
Chemotherapy is known for killing cancer cells, but it can also harm healthy cells in the body, including the good bacteria in the gut. These gut microbes are important for digestion, immune health, and now, scientists say, possibly even for helping the body handle toxic cancer drugs.
The UCSF team focused on a common class of chemotherapy drugs called fluoropyrimidines, often used to treat colorectal cancer.
The first study, published in Science Translational Medicine, found that while these powerful drugs reduced the diversity of gut bacteria in patients, some of the surviving bacteria were able to neutralize the drugs.
Instead of allowing the chemotherapy to damage the gut, these microbes “ate” the drugs and turned them into harmless substances. This helped lessen the symptoms patients often face during treatment, such as nausea and vomiting.
Kai Trepka, a medical student involved in the research, said it was remarkable to see how the gut bacteria adapted to protect the body. The researchers also found that by measuring how many of these helpful bacteria were present in a patient’s gut, they could predict who was likely to suffer more severe side effects.
To test the idea further, the team gave these protective bacteria to mice that were having bad reactions to chemotherapy. The mice’s symptoms improved, which suggests that similar bacteria could one day be given to human patients as a type of probiotic supplement to help them get through their treatment with fewer problems.
A second study, published in mBio, looked at another side effect of chemotherapy—nerve pain, often felt as numbness or tingling in the hands and feet. This condition, called neuropathy, can be very painful and sometimes long-lasting.
The researchers discovered that a type of bacteria that survived chemotherapy actually helped fight this symptom by producing vitamin K2, a nutrient known for its role in blood clotting and bone health.
When the researchers gave vitamin K2 to mice being treated with chemotherapy, their nerve-related symptoms got better. The team also found that human patients with fewer side effects tended to have more vitamin K2-producing bacteria in their guts. One of the helpful bacteria they identified was a safe strain of E. coli.
Dr. Wesley Kidder, one of the study’s authors, said this research is helping scientists understand how the gut microbiome—once seen as a mysterious “black box”—can be influenced to improve health outcomes.
By identifying which bacteria are helpful, and what substances they produce, researchers can begin to find new ways to support patients during tough treatments like chemotherapy.
In short, these two studies show that gut bacteria may not just survive chemotherapy—they might actually help the body deal with it. This discovery could lead to new treatments that reduce side effects and make cancer therapy easier to endure.
While more research and human testing are needed, the findings open the door to using probiotics and dietary supplements as tools in cancer care, alongside traditional drugs.
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The research findings can be found in Science Translational Medicine.
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