CCL2 and neoplasm: One of the most important external regulators are the tumor cells themselves as they can secrete M2-like cytokines such as IL-10, CCL2/3/4/5, CXCL12, VEGF, and platelet-derived growth factor (PDGF) to recruit monocytes and M0 macrophages to the tumor site and differentiate them into suppressive M2 TAMs (29, 30).