KDR and neoplasm: Bone marrow (BM) cells migrate to Ewing tumors and differentiate into the vascular smooth muscle/pericyte-like cells and endothelial cells expressing α-smooth muscle actin, desmin, and PDGFRβ, as well as a vascular endothelial growth factor (VEGFR)-2, and are subsequently associated with tumor vessel endothelium by PDFGRβ to support tumor vasculature (Reddy et al., 2008).