Tumor-Associated Macrophages as Major Immunosuppressive Cells in the Tumor Microenvironment

Abstract

Within the tumor microenvironment, myeloid cells constitute a dynamic immune population characterized by a heterogeneous phenotype and diverse functional activities. In this review, we consider recent literature shedding light on the increasingly complex biology of M2-like immunosuppressive tumor-associated macrophages (TAMs), including their contribution to tumor cell invasion and metastasis, stromal remodeling (fibrosis and matrix degradation), and immune suppressive functions, in the tumor microenvironment (TME). We also review the development of promising therapeutic approaches to target these populations in cancers. The expanding knowledge of distinct subsets of immunosuppressive TAMs, and their contributions to tumorigenesis and metastasis, has sparked significant interest among researchers regarding the therapeutic potential of TAM depletion or phenotypic modulation. This review delineates the involvement of M2-like TAM subsets in cancer development and metastasis, while also delving into the intricate signaling mechanisms underlying the polarization of diverse macrophage phenotypes, their plasticity, and therapeutic implications.