Molecular understanding and clinical aspects of tumor-associated macrophages in the immunotherapy of renal cell carcinoma

Renal cell carcinoma (RCC) is one of the most common tumors that afflicts the urinary system, accounting for 90-95% of kidney cancer cases. Although its incidence has increased over the past decades, its pathogenesis is still unclear. Tumor-associated macrophages (TAMs) are the most prominent immune cells in the tumor microenvironment (TME), comprising more than 50% of the tumor volume. By interacting with cancer cells, TAMs can be polarized into two distinct phenotypes, M1-type and M2-type TAMs. In the TME, M2-type TAMs, which are known to promote tumorigenesis, are more abundant than M1-type TAMs, which are known to suppress tumor growth. This ratio of M1 to M2 TAMs can create an immunosuppressive environment that contributes to tumor cell progression and survival. This review focused on the role of TAMs in RCC, including their polarization, impacts on tumor proliferation, angiogenesis, invasion, migration, drug resistance, and immunosuppression. In addition, we discussed the potential of targeting TAMs for clinical therapy in RCC. A deeper understanding of the molecular biology of TAMs is essential for exploring innovative therapeutic strategies for the treatment of RCC.