Tumor angiogenesis: molecular facts and therapeutic opportunities

Solid tumors do not grow beyond a size of a few millimetres without supply of nutrients and growth factors by the vascular system. Only when tumors pr oduce angiogenic growth factors new vessels are formed by sprouting of capi llaries from the existing vascular system. The tumor can grow and tumor cel ls reach the circulation through these new and permeable vessels. The vascu lar endothelial growth factor (VEGF) is the most prominent angiogenic growt h factor. VEGF is produced by almost all solid tumors: its receptors are ex pressed only on vascular endothelial cells and predominantly in vessels in the proximity of the tumor. Therefore, the VEGF/VEGF-receptor system is a t arget for anti-angiogenic cancer therapy. Experiments show that inhibition of the VEGF-mediated endothelial cell activation interferes with tumor grow th and metastases formation. Appropriate therapeutic strategies are current ly under clinical investigation.