Microbiome landscapes of the bladder, intestine, and vagina in bladder cancer: a systematic review

Microbiomes have been linked to oncogenesis, e.g. the intestinal microbiome and colon cancer or HPV-associated cervical cancer. A connection between microbiomes of different body cavities and tumor oncogenesis was shown. The gut microbiome’s influence on bladder cancer was established, raising the question whether nearby microbiomes (rectum, vagina) also influence bladder cancer due to their proximity. Considering the influence of various body cavities and the broader microbial components, this systematic review aims to investigate differences in the bladder, vaginal, and intestinal microbiota—including bacterial, viral, fungal and archaea—between patients with bladder cancer and healthy controls. Databases (PubMed, Scopus, Embase) were searched until April 2022. Three types of studies were included: “(1) studies using bladder cancer and control groups (case-controlled studies) (2) studies that provided information on the presence or abundance of microbial taxa (3) studies that provided information on increased or decreased taxa in bladder cancer and/or control groups.". Risk of bias was assessed using the Newcastle Ottawa Scale. Fourteen studies (695 samples: 403 bladder cancer, 292 controls) were analyzed. Bacterial taxa that have been detected in at least two studies, the genera Geobacillus and Rubrobacter were more frequently in bladder cancer patients; while Streptococcus and Roseomonas were more prevalent in controls. No consistent taxa were identified across stool or bladder tissue samples. The microbiota in bladder cancer patients show significant variation across studies. Standardized methods and expanded investigations into viral and fungal components are needed to clarify the role of microbiota in bladder cancer.