The gut microbiota plays a pivotal role in maintaining and regulating the intestinal microenvironment, characterized by its complexity and diversity. With the advancement of genomics and metabolomics technologies, increasing attention has been directed toward the involvement of gut microbiota in tumor initiation, progression, and therapeutic response. Emerging evidence suggests that the gut microbiota not only contributes to tumor development but also modulates the host immune system, thereby influencing antitumor immune responses and enhancing immunotherapy efficacy. A growing body of studies has demonstrated close associations between the gut microbiota, tumor immunotherapy, and related adverse events. Consequently, the gut microbiota holds great potential as a predictive biomarker for tumor occurrence and as a critical regulatory factor affecting immunotherapy outcomes. This review summarizes recent advances in the field, highlighting the interplay between the gut microbiota and tumor immunity, and provides novel perspectives for leveraging gut microbiota to optimize cancer immunotherapy.

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