Breast cancer exosomes: Managing macrophage polarization and immune regulation in the tumor microenvironment

Exosomes are sub-150 nm extracellular vesicles mediating intercellular messaging in breast cancer's complex tumor microenvironment (TME). Produced by both tumor cells and their stroma components, these vesicles excrete various biomolecules, such as microRNAs (miRNAs), proteins, lipids, and even DNA fragments, enabling a functional exchange of information among cells. In breast cancer, different studies indicate a significant role of exosome-mediated signaling in modulating the phenotype of tumor-associated macrophages (TAMs), mainly polarizing them toward an M2-like phenotype, further supporting the potentiality for tumor-promoting functions. This review will detail the diverse roles of breast cancer-derived exosomes and macrophage polarization and elaborate on their recognized pathways by which these vesicles casually alter the macrophage phenotype. In our discussion, we take a broad detour to deeply examine the unique molecular accessories delivered by breast cancer exosomes. In particular, we discuss the miRNAs suppressed by M1-associated gene expression and those endowing M2-related pathways with abilities, and we cover the proteins that activate pathways like the STAT3 and NF-κB pathways in macrophages. This review will also address the relevance of mechanistic issues to clinical manifestation in exosome-mediated macrophage polarization in breast cancer. Finally, targeting exosome-mediated macrophage polarization as a promising strategy to enhance antitumor immunity in conjunction with improving breast cancer outcomes is deliberated.