CCL2 and neoplasm: However, in the tumor microenvironment, malignancies recruit circulating monocytes by producing tumor-derived chemotactic factors such as macrophage chemoattractant protein-1 (MCP-1), vascular endothelial growth factor (VEGF), and macrophage colony-stimulating factor (MCSF) and then induce monocytes to differentiate into tumor-associated macrophages (TAMs) [5].