Fig. 1

The origin and evolution of TAMs. TAMs stem from bone marrow-derived circulating monocytes and embryonic tissue-resident macrophages (TRM). Regulatory molecules (including CCL2, CCL5, CCL7, CCL16, CCL20, CXCL8, CXCL12, CSF, IL-1β, IL-6, IL-17, IL-33, IL-34, TGF-β, TNF, PGE2, VEGF, PDGF and SLIT2) induce the recruitment of monocytes/macrophages to tumor tissues. Upon recruitment to the TME, these cells are stimulated by various signals to polarize into M1 or M2-like macrophages and then exhibit diverse functions