Probiotics and postbiotics in colorectal cancer: Prevention and complementary therapy

Colorectal cancer (CRC) is a leading cause of human mortality worldwide. As conventional anticancer therapy not always being effective, there is growing interest in innovative "drug-free" cancer treatments or interventions that improve the efficacy of established therapy. CRC is associated with microbiome alterations, a process known as dysbiosis that involves depletion and/or enrichment of particular gut bacterial species and their metabolic functions. Supplementing patient treatment with traditional probiotics (with or without prebiotics), next-generation probiotics (NGP), or postbiotics represents a potentially effective and accessible complementary anticancer strategy by restoring gut microbiota composition and/or by signaling to the host. In this capacity, restoration of the gut microbiota in cancer patients can stabilize and enhance intestinal barrier function, as well as promote anticarcinogenic, anti-inflammatory, antimutagenic or other biologically important biochemical pathways that show high specificity towards tumor cells. Potential benefits of traditional probiotics, NGP, and postbiotics include modulating gut microbiota composition and function, as well as the host inflammatory response. Their application in CRC prevention is highlighted in this review, where we consider supportive in vitro, animal, and clinical studies. Based on emerging research, NGP and postbiotics hold promise in establishing innovative treatments for CRC by conferring physiological functions via the production of dominant natural products and metabolites that provide new host-microbiota signals to combat CRC. Although favorable results have been reported, further investigations focusing on strain and dose specificity are required to ensure the efficacy and safety of traditional probiotics, NGP, and postbiotics in CRC prevention and treatment.