Gut microbiota and chemoradiotherapy response in rectal cancer: Biomarker opportunities

The gut microbiota is increasingly recognized as a key factor in rectal carcinogenesis. This review synthesizes current clinical and preclinical evidence linking specific microbial signatures, such as Fusobacterium nucleatum, Duodenibacillus massiliensis and colibactin-producing Escherichia coli (CoPEC) to chemoradiotherapy (CRT) treatment efficacy and resistance. Microbiota-driven mechanisms include immune modulation, inflammation, and drug metabolism. We highlight emerging microbial biomarkers and therapeutic strategies such as antibiotics, probiotics, and fecal microbiota transplantation. Integrating microbiome profiling into clinical workflows could refine patient stratification and enhance CRT efficacy in rectal cancer. Ongoing clinical trials aim to validate these associations and establish robust microbial biomarkers for CRT response prediction in rectal cancer.