Systematic review: The mucosa-associated microbiota in colorectal cancer

Abstract

Background: The intestinal microbiome has been associated with colorectal cancer. Although the mucosal microbiota is a better representation of an individual's local microbiome, studies on the colorectal cancer microbiota mainly reflect knowledge obtained from faecal samples. Aim: This systematic review aimed to summarize the current evidence on the relationship between the mucosal-associated bacterial microbiota and colorectal cancer. Methods: Searches were conducted in the PubMed and Web of Science databases for publications that compare the mucosal microbiome of colorectal cancer patients with that of healthy controls, or with that of non-cancerous mucosal tissues. The primary outcomes were differences in microbial diversity and taxonomy. The Newcastle-Ottawa Scale was used to assess the quality of the included studies. Results: Of the identified 3724 studies, 32 were eligible and included in the systematic review. No consistent results between studies were identified for the α-diversity and β-diversity, but four out of five studies showed that the structure of the mucosal microbiota could distinguish colorectal cancer patients from healthy controls. Qualitative synthesis of microbial taxonomy results identified 11 bacteria taxa with strong positive and 10 taxa with strong negative associations with colorectal cancer. <i>Fusobacterium</i>, <i>Streptococcus</i>, <i>Campylobacter</i>, <i>Parvimonas</i>, <i>Peptostreptococcus</i>, and <i>Granulicatella</i> were defined as enriched in colorectal cancer. Conclusion: Despite the methodological limitations of the studies, consistent evidence on bacteria taxa associated with colorectal cancer was identified. Prospective studies in large and well-characterized patient populations will be crucial to validate these findings.