Probiotic Administration Modulates Gut Microbiota and Suppresses Tumor Growth in Murine Models of Colorectal Cancer

Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide with limited treatment options for advanced disease stages. Growing evidence implicates the gut microbiota in CRC pathogenesis, prompting interest in probiotics as a potential therapeutic strategy. In this study, we evaluated the effects of two probiotic compositions, CI (a mix of <i>lactobacilli</i> and <i>bifidobacteria</i>) and CII (<i>bifidobacteria alone</i>), in two murine CRC models: the orthotopic MC-38 cecum injection model and the inflammation-driven azoxymethane/dextran sodium sulfate (AOM/DSS) model. CI showed significant anti-tumor effects in the orthotopic model, reducing tumor weight and volume, which was, however, not associated with robust immune activation, suggesting microbiota-driven mechanisms. In contrast, CII was more effective in the AOM/DSS model, reducing colonic inflammation and completely preventing tumor development. Our study demonstrates that probiotics might have great therapeutic potential via modulation of the gut microbiota, and they can exert anti-tumor effects in murine models of CRC with distinct compositions showing differential efficacy depending on the model. CI stabilized the gut microbiome and inhibited pro-tumorigenic taxa in the MC-38 cecum injection model, while CII exhibited anti-inflammatory properties in the AOM/DSS model, highlighting the potential of probiotics as context-specific interventions for CRC. These findings contribute to the growing body of evidence supporting microbiota-targeted strategies in oncology and their relevance for therapeutic applications.