Probiotics in colorectal cancer: mechanisms, biomarkers, and adjunct strategies

Colorectal cancer (CRC) is among the most common malignant tumors and remains a leading cause of cancer-related mortality worldwide. The gut microbiota and metabolites, which are modulated by host genetics and environmental exposures, have emerged as key contributors to the pathogenesis of CRC. A key feature of gut dysbiosis in CRC is the enrichment of pathogenic bacteria alongside the depletion of beneficial commensals. Probiotic supplementation has been shown to counteract this imbalance and suppress tumor progression. Mechanistically, probiotics suppress CRC development through multifaceted actions, including directly inhibiting tumor cell growth, reducing inflammation, reinforcing the intestinal barrier, and reprogramming host immunity. This review summarizes evidence on the inhibitory role of probiotics in CRC, evaluates the potential of probiotics as predictive biomarkers, and discusses microbiome-modulation strategies designed to enhance immunotherapy and chemotherapy, thereby offering a complementary paradigm for CRC prevention and treatment.