CCL2 and cancer: It is known that many types of cancer cells secret a large range of extracellular mediators, including cytokines, chemokines and growth factors, such as the chemokine (C-C motif) ligand 2 (CCL2), IL-6, transforming growth factor beta (TGF-β), tumor necrosis factor alpha (TNF-α), matrix metalloproteinases (MMPs), and granulocyte-macrophage colony-stimulating factor (GM-CSF) (41, 42).