Increasing evidence shows that bone marrow-derived monocytes can be recruited and differentiated into TAMs by a variety of chemokines and growth factors released by tumor cells and stromal cells in the TME, such as C-C chemokine ligand 2 (CCL2), CCL5, CCL7, C-X-C motif chemokine ligand 8 (CXCL8), CXCL12, granulocyte macrophage colony stimulating factor (GM-CSF), macrophage colony promoting factor (M-CSF), vascular endothelial growth factor (VEGF), and platelet derived growth factor (PDGF) [15, 16]. The gene discussed is CCL2; the disease is neoplasm.