CCL2 and neoplasm: The activation modes and markers of TAMs in different tumor tissues are diverse; thus, it is still not clear exactly what induces TAMs, but possibilities include combinations of vascular endothelial growth factors (VEGFs), tumor growth factor (TGF)-β, interleukin (IL)-4, C-C motif chemokine ligand 2 (CCL2), colony-stimulating factors (CSFs), and some extracellular matrix components.