CCL2 and melanoma: Melanoma-associated macrophages can derive either from embryonic-derived tissue resident macrophages (Res-TAMs), recruited and maintained by colony-stimulating factor-1 (CSF-1) binding its receptor CSF1R,25 or through the recruitment of circulating monocytes via the CCL2/CCR2 chemokine pathway, which can differentiate into monocyte-derived macrophages (mo-TAMs).26–28 The exact contributions of each origin pool are still being explored, with a paucity of information on how macrophage ontogeny affects TAM function within melanoma.