Gut Microbiota in Colorectal Cancer: Associations, Mechanisms, and Clinical Approaches

Colorectal cancer (CRC) is associated with the presence of particular gut microbes, as observed in many metagenomic studies to date. However, in most cases, it remains difficult to disentangle their active contribution to CRC from just a bystander role. This review focuses on the mechanisms described to date by which the CRC-associated microbiota could contribute to CRC. Bacteria like pks+ Escherichia coli, Fusobacterium nucleatum, or enterotoxigenic Bacteroides fragilis have been shown to induce mutagenesis, alter host epithelial signaling pathways, or reshape the tumor immune landscape in several experimental systems. The mechanistic roles of other bacteria, as well as newly identified fungi and viruses that are enriched in CRC, are only starting to be elucidated. Additionally, novel systems like organoids and organs-on-a-chip are emerging as powerful tools to study the direct effect of gut microbiota on healthy or tumor intestinal epithelium. Thus, the expanding knowledge of tumor-microbiota interactions holds promise for improved diagnosis and treatment of CRC.