CSF2 and neoplasm: Tumors often secrete a range of cytokines and chemokines that promote MDSC development and recruitment to the tumor microenvironment such as granulocyte-macrophage colony-stimulating factor (GM-CSF), which stimulates the generation of MDSCs from bone marrow precursors [197]; interleukin 6 (IL-6), which promotes MDSC expansion and survival [198]; and VEGF, which attracts MDSCs to the tumor site and promotes their survival [199].