Involvement of protumor macrophages in breast cancer progression and characterization of macrophage phenotypes.

Tumor-associated macrophages (TAMs) are the most prominent immune cells in the breast cancer microenvironment, and the protumor functions of TAMs are thought to affect cancer progression and resistance to anti-cancer therapy. Numerous studies using human breast cancer samples, cell lines, and murine breast cancer models have revealed details of the mechanisms by which the protumor functions of TAMs are activated. Recent advances have highlighted the significant involvement of TAMs in the resistance of breast cancer cells to immunotherapy. TAMs express a number of immunosuppressive genes, and single-cell sequence analyses of human and murine cancer samples have helped elucidate the mechanism of TAM-induced immunosuppression. As TAMs are considered suitable targets for anti-cancer therapies, we summarized the protumor functions of TAMs and the potential of anti-cancer therapies targeting TAMs, with a focus on breast cancer research.