VEGFA and neoplasm: Several potential mechanisms of resistance to anti-angiogenic drugs like sunitinib have been proposed and two main types of resistance can be distinguished: resistance of the tumor vasculature to the inhibition of VEGF and PDGF signaling (vascular resistance); and resistance of cancer cells to the hypoxic and nutrient-depleted microenvironment induced by anti-angiogenic effects (hypoxia resistance - resistance to the effector mechanism of anti-angiogenic treatment).