Decoding the dual roles of monocytes in tumor immunity: from immunosurveillance to immune evasion

Monocytes are innate immune cells of the mononuclear phagocyte system, extensively involved in immune and inflammatory responses, and play a critical regulatory role in tumor development and progression. Different monocyte subsets can exert either pro-tumor or anti-tumor functions by modulating immune responses. Through the secretion of cytokines and chemokines, monocytes regulate immune activity, while tumor cells utilize these signaling pathways to influence monocyte polarization, inducing their transformation into immunosuppressive phenotypes. The origin, migration, polarization, and transformation of monocytes within the tumor microenvironment represent key research areas in current cancer immunotherapy. Precise regulation of monocyte function holds promise for developing novel strategies in tumor immunotherapy. Current approaches, such as monocyte-mediated vaccines and combination therapies with immune checkpoint inhibitors, have emerged as major research focuses in cancer immunotherapy. This review summarizes the mechanisms by which monocytes regulate antitumor immune responses and discusses recent advances in their therapeutic applications.