CSF2 and neoplasm: In contrast to these RT-induced immunostimulatory effects, RT can also induce immunosuppressive responses, such as the secretion of immune suppressive cytokines (i.e. granulocyte-macrophage colony-stimulating factor, GM-CSF; transforming growth factor-β, TGF-β) from tumor cells, which promote the migration of myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Treg) from the circulation towards irradiated areas (16).