The impact of the gut microbiota on prognosis after surgery for colorectal cancer - a systematic review and meta-analysis.

Palmgren Colov, Emilie; Helene Degett, Thea; Raskov, Hans; Gögenur, Ismail

The aim of this study was to conduct a systematic review of the association between gut microbiota and prognosis after colorectal cancer surgery. The review was conducted according to the PRISMA guidelines. A systematic literature search was conducted in PubMed, Embase and Scopus. Studies examining the association between gut microbiota and survival after colorectal cancer surgery were identified. Secondary outcomes were association with cancer stage and immune infiltration of tumor. A total of 27 studies were included in the review. Fusobacterium nucleatum was the most frequently examined bacterium and the meta-analysis showed that high level of Fusobacterium nucleatum was significantly associated with decreased overall survival, hazard ratio 1.63 (95% confidence interval 1.23-2.16) for unadjusted data and hazard ratio 1.47 (95% confidence interval 1.08-1.98) for adjusted data. Association between higher tumor stage and Fusobacterium nucleatum was reported in ten studies and two studies found an association with unfavorable tumor infiltration of immune cells. Three out of five studies examining Bacteroides fragilis found an association with decreased survival, advanced tumor stage or unfavorable immune infiltration of tumor. High levels of Fusobacterium nucleatum and possibly Bacteroides fragilis was associated with worse prognosis after surgery for colorectal cancer.