Abstract
Stromal immune cells constitute the tumor microenvironment. These immune cell subsets include myeloid cells, the so-called tumor-associated myeloid cells (TAMCs), which are of two types: tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs). Breast tumors, particularly those in human epidermal growth factor receptor 2 (HER-2)-positive breast cancer and triple-negative breast cancer, are solid tumors containing immune cell stroma. TAMCs drive breast cancer progression via immune mediated, nonimmune-mediated, and metabolic interactions, thus serving as a potential therapeutic target for breast cancer. TAMC-associated breast cancer treatment approaches potentially involve the inhibition of TAM recruitment, modulation of TAM polarization/differentiation, reduction of TAM products, elimination of MDSCs, and reduction of MDSC products. Furthermore, TAMCs can enhance or restore immune responses during cancer immunotherapy. This review describes the role of TAMs and MDSCs in breast cancer and elucidates the clinical implications of TAMs and MDSCs as potential targets for breast cancer treatment.
Highlights
Breast cancer is one of the most common malignant tumors among women and a major cause of mortality among women worldwide [1]
This review describes the role of tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs) in breast cancer and elucidates the clinical implications of TAMs and MDSCs as potential targets for breast cancer treatment
The tumor microenvironment (TME) in breast cancer plays an important role in tumor development, progression, and metastasis [5,6], and tumor-associated myeloid cells (TAMCs) are further involved in physiological phenomena in breast tumors
Summary
Breast cancer is one of the most common malignant tumors among women and a major cause of mortality among women worldwide [1]. Immunosuppressive mechanisms in tumor cells via MDSCs are as follows: monocytic-MDSCs express inducible nitric oxide synthase (iNOS) and generate nitric oxide (NO), while granulocytic-MDSCs produce reactive oxygen species (ROS) and arginase. Cytokines and chemokines promote MDSC accumulation at tumor sites in breast cancer These cytokines include IL-6 [46], IL-1β [47], G-CSF [48], M-CSF [49], GM-CSF [50], macrophage. These cytokines include IL-6 [46], IL-1β [47], G-CSF [48], M-CSF [49], GM-CSF [50], macrophage Migration Inhibitory Factor (MIF) [51], and TGF-1β [52], and the reported chemokines. 2020, 9, 1785 are [53], CCL1 [47], CCL2 [54], and CCL5 [55]
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