CCL2 and neoplasm: Tumor and stroma-derived growth factors and cytokine regulating stemness and resistance comprise interleukin-6 (IL-6), interleukin-8 (IL-8), chemokine (C-X-C motif) ligand 12 (CXCL12), chemokine (C-X-C motif) receptor type 4 (CXCR4), chemokine (C-C motif) ligand 2 (CCL2), platelet-derived growth factor (PDGF), transforming growth factor-beta 1 (TGF-β1), tumor necrosis factor-alpha (TNFα), epidermal growth factor (EGF), VEGF and fibroblast growth factor (FGF) (62, 126).