Gut Microbiota in Colorectal Cancer: Mechanisms of Carcinogenesis, Biomarkers, and Therapeutic Perspectives.

Colorectal cancer (CRC) remains one of the leading causes of cancer-related mortality worldwide, largely due to late-stage diagnosis and the limited sensitivity of current screening approaches for early lesions. In recent years, the gut microbiota has emerged as a key factor in colorectal carcinogenesis, offering promising opportunities for the development of novel, non-invasive diagnostic and therapeutic strategies. Specific bacterial species and microbial metabolites have been implicated in colorectal carcinogenesis and are under investigation as potential biomarkers for CRC detection. However, despite growing evidence of association, most remain investigational and require further clinical validation before routine implementation. Among the proposed bacterial biomarkers, Fusobacterium nucleatum is one of the most promising candidates for clinical implementation, with encouraging evidence supporting its use in non-invasive stool-based CRC detection. Streptococcus gallolyticus subsp. gallolyticus and Clostridium septicum currently serve primarily as clinical warning markers due to their well-established association with occult colorectal malignancy rather than as screening biomarkers. In contrast, pks+Escherichia coli, enterotoxigenic Bacteroides fragilis, Enterococcus faecalis, and Peptostreptococcus anaerobius remain investigational. Helicobacter pylori has limited value for CRC detection because of its inconsistent association and low specificity. Overall, this review summarizes the most extensively studied bacterial species and microbial metabolites involved in colorectal cancer development, with particular emphasis on their underlying pathogenic mechanisms and highlighting their potential value as diagnostic biomarkers and therapeutic targets. It also highlights emerging bacterial taxa and microbial signatures that have been associated with early tumorigenesis in recent studies.