M2 macrophages secrete chemokine (C–C motif) ligand 2 (CCL2)/monocyte chemoattractant protein-1 (MCP-1) [11], which promotes tumor growth by binding and activating C–C chemokine receptors type 2 (CCR2), type 4 (CCR4), and type 5 (CCR5) [13] expressed on certain immune cells, endothelial cells, cancer-associated fibroblasts, and tumor cells. Here, CCL2 is linked to cancer.