in the Colorectum and Its Association with Cancer Risk and Survival: A Systematic Review and Meta-analysis.

Background: The gut microbiome, in particular , has been reported to play a role in colorectal cancer development and in patient prognosis. We aimed to perform a systematic review and meta-analysis of published studies to assess the prevalence of in colorectal tumors and evaluate the association between and colorectal cancer development and prognosis.

Methods: MEDLINE, EMBASE, and Web of Science databases were systematically searched for studies published until January 2019. Random effects meta-analyses were used to assess the prevalence of in patients with colorectal cancer or tissues relative to controls and survival in -positive versus -negative patients.

Results: Forty-five relevant articles were identified. Meta-analyses indicated higher odds of being present in colorectal tissue samples from patients with colorectal cancer [ = 6 studies, pooled OR = 10.06; 95% confidence intervals (CI), 4.48-22.58] and individuals with colorectal polyps ( = 5 studies, pooled OR = 1.83; 95% CI, 1.07-3.16) compared with healthy controls. Similar results were apparent in fecal samples, and when comparing tumor with adjacent normal tissue. Meta-analyses indicated poorer survival in patients with colorectal cancer with high versus low abundance ( = 5 studies, pooled HR = 1.87; 95% CI, 1.12-3.11).

Conclusions: A consistent increase in the prevalence and/or abundance of in colorectal cancer tissue and fecal samples compared with controls was apparent. High abundance of in colorectal tumors was also associated with poorer overall survival.

Impact: could be useful as a diagnostic and prognostic marker for colorectal cancer or as a treatment target.