Current evidence on the role of urinary microbiome in bladder cancer: A narrative review

Abstract

For decades, urine was thought to be sterile, and any bacteria found in it were thought to be due to an infection. However, new sequencing technologies have changed this view and shown that even healthy people have a unique urinary microbiome. To understand how this urinary microbiome may relate to bladder cancer, we reviewed human studies that characterized urinary microbial profiles in patients with bladder cancer using culture-independent and enhanced culture-based methods. Across the literature, bladder cancer is consistently associated with shifts in microbial community structure, including loss of bacteria thought to support mucosal health and enrichment of organisms linked to inflammation and epithelial injury. Several studies further suggest that specific urinary microbial patterns correlate with tumor presence, risk of recurrence, and even response to intravesical and systemic immunotherapy, raising the possibility that the microbiome influences disease behavior rather than merely reflecting it. Proposed mechanisms include altered immune signaling within the bladder, production of pro-carcinogenic metabolites, and disruption of the urothelial barrier that may promote chronic inflammation. Taken together, the available data suggest that bladder cancer does not develop in isolation but within a dynamic microbial environment that may shape tumor biology and treatment responses. Larger, prospective studies using standardized bladder-specific sampling are needed to determine whether urinary microbiome alterations are drivers of carcinogenesis or consequences of tumor-induced changes and to evaluate their potential as non-invasive biomarkers and therapeutic targets.