Angiogenesis is regulated by the highly coordinated function of various proteins 
with pro- and antiangiogenic functions. Proangiogenic factors include vascular 
endothelial growth factor (VEGF), fibroblast growth factor, platelet-derived 
growth factor, insulin-like growth factor, transforming growth factor, 
angiopoietins, and several chemokines; antiangiogenic factors include 
thrombospondin-1, angiostatin, and endostatin. Matrix metalloproteinases display 
a dual role in vascular development. Notch signaling affects remodeling of the 
primary vascular network of uniformly sized vessels into functionally and 
morphologically distinct arteries, veins, and capillaries. Tumors, described as 
'wounds that never heal', lose the appropriate balance among these factors. 
Although VEGF-targeted therapies are showing promise, new angiogenesis targets 
are needed to make additional gains. Here, we highlight recent advances in our 
understanding of the regulation of tumor angiogenesis and discuss the potential 
of molecular targeting as a new therapeutic approach.