KITLG and neoplasm: MDSCs can be induced in vitro by various tumour-derived substances, including prostaglandin E2, interleukin-6, interleukin-10, interleukin-1, transforming growth factor (TGF), stem cell factor (SCF), and pro-angiogenic factors, including vascular endothelial growth factor (VEGF) [15, 16, 23, 24].