In May 2026, City of Hope convened HHS Secretary Robert F. Kennedy Jr., NIH Director Jay Bhattacharya, NCI leaders and representatives from leading cancer centers to discuss the microbiome's role in cancer prevention and treatment. Discussions focused on strengthening cancer research, expanding clinical trials, increasing access to care and accelerating the translation of scientific discoveries into patient care. The symposium reflects City of Hope's broader commitment to advancing research, nutrition, prevention and precision medicine to improve outcomes for patients.
City of Hope’s CEO Robert Stone spoke of the microbiome as one of the next great frontiers in medical science. U.S. Health and Human Services Secretary Robert F. Kennedy expressed his desire to see the microbiome become a major national research priority because of its potential role in cancer, immune function, chronic disease and treatment outcomes. Among the centers represented were City of Hope, the National Cancer Institute, the University of Texas MD Anderson Cancer Center, Memorial Sloan Kettering Cancer Center, Dana-Farber Cancer Institute, University of Pennsylvania’s Perelman School of Medicine, Roswell Park Comprehensive Cancer Center, and Fred Hutch Cancer Center.
Watch a short video summary of the day.
Here are 5 takeaways from the research presentations:
1. The microbiome strongly influences cancer immunotherapy outcomes.
Multiple presenters showed that patients with healthier, more diverse gut microbiomes tend to have better responses to chimeric antigen receptor (CAR) T-cell therapy, immune checkpoint inhibitors, and combination immune therapies. Conversely, antibiotic exposure can lead to worse outcomes, as they are associated with reductions in microbiome diversity.
A recurring theme: the tumor is not the whole story — part of immunotherapy response may be determined by what's happening in the gut.
2. Diet offers a practical microbiome intervention.
Multiple teams presented evidence that dietary modification can act as a tool to improve immune function and potentially improve cancer outcomes. High-fiber diets increased microbiome diversity.
Particularly important findings:
- High-fiber diets increased microbiome diversity — a key driver of better outcomes.
- Fiber diet consumption increased “good” bacteria — for example, the bacteria that produce butyrate, a molecule with anti-cancer, anti-inflammation properties.
- Plant-based dietary interventions reduced inflammatory markers.
- In one fiber diet study, dietary improvements continued well after plant-based dietary interventions had ended.
3. Across multiple studies and cancer types, butyrate appears to be a common biological mechanism linking diet, microbiome composition and immune outcomes.
Butyrate is a byproduct of the fermentation of fiber and appears to bring cancer-fighting benefits including reduced inflammation, improved immune function, enhanced anti-tumor responses, and an association with favorable microbiome composition. For instance, in multiple myeloma patients, a high fiber diet increased butyrate-producing bacteria.
City of Hope and other cancer research centers are continuing to evaluate the role of this short-chain fatty acid in our health and identify ways to boost its effectiveness.
4. An ancient remedy is pointing the way to a modern understanding of the microbiome's role in cancer outcomes.
Fecal microbiota transplantation (FMT) is the process of transferring fecal bacteria and other microbes from a healthy individual into an unhealthy individual. While the use of fecal transfer as a therapeutic intervention can be traced back to 4th century China, researchers at the symposium highlighted its modern-day relevance by demonstrating that microbiome transfer (in the form of a pill) can directly influence cancer treatment responses. For example:
- Melanoma patients resistant to immunotherapy regained responsiveness after receiving FMT from patients who responded well to immunotherapy.
- FMT from an exceptional responder transferred cancer benefit into mice.
- Ovarian cancer studies demonstrated transfer of immunotherapy responsiveness through FMT.
Bottom line: the microbiome is not merely associated with outcomes; it can drive them.
However, speakers agreed that FMT is unlikely to be scalable for millions of patients and should be viewed primarily as a proof-of-concept tool.
5. Personalized microbiome oncology is coming.
Differences in gut bacteria may help explain why patients with similar cancers can experience different outcomes from the same treatment. Because the microbiome can be measured and modified, researchers are exploring whether it could become an important tool for personalizing cancer care.
Future clinical practice may include:
- Microbiome profiling before treatment
- Dietary assessments as standard intake procedures
- Precision nutrition plans
- Microbiome therapeutics tailored to patient biology
The field appears to be moving toward a future where microbiome assessment, nutrition, and microbiome-directed therapies become integrated into standard oncology care alongside drugs, surgery, radiation and cellular therapies.
The Bottom Line
The microbiome is emerging as an important factor in cancer care, influencing how patients respond to treatment, recover and experience side effects. City of Hope is committed to supporting the scientific leadership, clinical research and national collaborations needed to advance this promising new frontier in care.