 Sunitinib is a potent inhibitor of the tyrosine kinase activity of several receptors: VEGFR-2, the main receptor responsible for mediating the proangiogenic effects of vascular endothelial growth factor VEGF, expressed by vascular endothelial cells; PDGFR, the receptor for the platelet-derived growth factor PDGF, expressed in pericytes which serve as structural supporting cells for endothelial cells. Consistent with its biochemical activity, Sunitinib inhibits the in vitro mitogenic response of human umbilical vein endothelial cells HUVECs stimulated by VEGF or bFGF basic fibrosblast growth factor, another proangiogenic factor. 