TGFB1 and neoplasm: There are many tumor-derived factors that can promote the expansion of MDSCs through the stimulation of myelopoiesis and inhibit the differentiation of mature myeloid cells, such as vascular endothelial growth factor (VEGF), prostaglandin E2 (PGE2), granulocyte-macrophage colony-stimulating factor (GM-CSF), transforming growth factor-β (TGF-β), interleukin- (IL-) 1β, IL-10, IL-6, and macrophage colony-stimulating factor (M-CSF) [6].