Immunotherapy has transformed treatment for advanced renal cell (kidney) cancer, but for many patients, it can cause significant side effects that sometimes lead to treatment delays or interruptions. New research is exploring whether improving gut health could make these treatments work better and more safely.
In a small early-phase clinical trial, researchers tested whether fecal microbiota transplantation (FMT), a procedure that introduces healthy gut bacteria from a screened donor, could help patients with metastatic renal cell (kidney) cancer respond better to immunotherapy.
What did the study look at?
The phase 1 study included 20 patients with advanced renal cell (kidney) cancer who hadn’t yet received treatment. Patients were given standard immunotherapy combinations along with capsules containing gut bacteria from carefully screened healthy donors. The main goal was to see whether this approach was safe, while also looking at how well the cancer responded, how the immune system behaved, and how patients felt during treatment.
What did the study find?
The results were encouraging. The treatment approach was found to be safe, with no life-threatening immune-related side effects and no serious complications linked to FMT. While some patients did experience moderate immune-related side effects, something commonly seen with immunotherapy, these were manageable. Only one person reported mild digestive symptoms related to the microbiome treatment.
Among patients whose tumors could be evaluated, half experienced tumor shrinkage, and two patients saw their cancer disappear on scans. Overall, about two-thirds of patients achieved meaningful disease control that lasted at least six months.
Why the gut microbiome matters
When researchers looked more closely at patients’ gut bacteria, they found a clear pattern. Those who developed a more diverse and anti-inflammatory microbiome after FMT were less likely to experience severe immune-related side effects and more likely to benefit from immunotherapy. This suggests that gut health may influence how the immune system responds to cancer treatment.
The study also highlighted that not all bacteria are helpful in this setting. Certain microbial patterns were linked to higher toxicity, underscoring the importance of careful donor screening and targeted approaches rather than one-size-fits-all solutions.
What this means for patients
Although this was a small, early-stage study, the encouraging data suggests gut health may help improve how well immunotherapy works while reducing unwanted side effects.
For now, FMT isn’t a part of standard renal cell (kidney) cancer treatment, and more research is needed before it becomes widely available. Still, these findings offer hope that combining immunotherapy with microbiome-based strategies could help more patients stay on treatment longer and experience better outcomes.
Want to learn more about the latest treatment advances in renal cell (kidney) cancer? Check out our “Ask the Expert” webinar with Dr. Toni Choueiri.
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