CCL2 and cancer: Numerous cytokines and chemokines, such as TNF, IL-6, IL-8, CXCL12, TGF-β, CXCL8, VEGF, RANKL, CCL2, CX3CL1, IL-1, IL-7, CXCL1, and CXCL16, contribute to the regulation of cancer metastasis [44, 45].