CSF2 and melanoma: Generation, expansion, and recruitment of MDSC to the TME is influenced by cytokines, chemokines and growth factors produced by melanoma and host cells such as interleukin (IL)-1β, IL-6, IL-8, vascular endothelial growth factor (VEGF), macrophage colony-stimulating factor (M-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) (9, 13).