CSF2 and neoplasm: Under the stimulation of granulocyte colony-stimulating factor (G-CSF), GM-CSF, pro-inflammatory cytokines interleukin-6 (IL-6), IL-8, TGF-β, and leukotriene B4, immature PMN-MDSCs undergo massive expansion from their precursors in the bone marrow and venture into the peripheral blood and tumor microenvironment [12–17].