In the process of cancer development, CCL2 together with macrophage-colony stimulating factor (M-CSF) and vascular endothelial growth factor (VEGF) play an active role to recruit circulating blood monocytes to the tumor site, where the recruited monocytes will be differentiated into tumor-associated macrophages (TAM) and establish a symbiotic relationship with the tumor cells. This evidence concerns the gene CCL2 and cancer.