The recruitment and polarization of TAMs are driven by a series of growth factors, including CSF-1, granulocyte-macrophage colony-stimulating factor (GM-CSF) and CCL2, which are secreted by tumor cells and TAMs, and then produce epidermal growth factor (EGF), MMP-9, MMP-2 and urokinase plasminogen activator (uPA) to promote tumor cell metastasis [126,127]. The gene discussed is CCL2; the disease is neoplasm.