CXCR4 and neoplasm: The formation of tumor-associated vessels is facilitated and accelerated by vasculogenesis, a process which generally takes place during embryo life, involving the endothelial cell precursors: the latter are bone-marrow resident immature cells which, as for mature endothelial cells express both the type 2 VEGF receptor and the chemokine receptor CXCR4 (68, 136).