How to cite: Liss MA. Microbiome in Bladder Cancer. Grand Rounds in Urology. November 2025. Accessed Jan 2026. https://grandroundsinurology.com/microbiome-in-bladder-cancer/
Summary
Michael A. Liss, MD, PhD, MAS, FACS, Professor of Urology, University of California, San Diego, San Diego, California, examines the growing evidence that the microbiome contributes to bladder cancer development and progression. He emphasizes that, beyond genetics, age, smoking, and environmental exposure, the bacterial composition of the urinary tract represents a new modifiable risk factor.
Dr. Liss explains that the bladder is not sterile. Microbial communities persist within and beneath urothelial cells. Healthy microbiomes often contain Lactobacillus and Corynebacterium, which are associated with balanced immune tolerance. In contrast, pathogens such as Streptococcus and Actinobacterium promote inflammation and tumor formation. Increased microbial diversity, measured by the Shannon Index, correlates with longer recurrence-free survival.
He presents data showing that reduced microbial diversity and enrichment of Pseudomonas species predict poorer outcomes. Some bacterial species metabolize chemotherapy drugs, directly affecting efficacy. For instance, E. coli can degrade gemcitabine, rendering it inactive, while eliminating these bacteria with ciprofloxacin restores the drug’s antitumor effect. However, indiscriminate antibiotic use may also impair beneficial microbial interactions and reduce the response to BCG or immunotherapy.
Dr. Liss reviews studies that show certain microbes modulate immune activity through PD-L1 expression and antigen presentation, thereby influencing the outcomes of checkpoint inhibitors. He highlights ongoing trials testing fecal microbiota transplant (FMT) and probiotic supplementation to enhance the immune response, first in renal cell carcinoma and now in bladder cancer.
Dr. Liss emphasizes that microbiome modulation represents a new frontier in therapeutic approaches. Future research will clarify how bacterial signatures predict therapy response and how selective microbial interventions, such as probiotics, bacterial peptides, or dietary modification, can improve bladder cancer outcomes.
ABOUT THE AUTHOR
Michael A. Liss MD, PhD, MAS, FACS, is a Professor of Urology and the Director of Clinical Trials in the Center for Microbiome Innovation at the University of California, San Diego. Dr. Liss specializes in Genitourinary Cancers, Kidney Cancer, Prostate Cancer, and Prostate Cancer Surgery. His primary research interests include incorporating imaging and biomarker translational research into interventional clinical trials.
