[In Process Citation]

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 produce angiogenic growth factors new vessels are formed by sprouting of capillaries from the existing vascular system. The tumor can grow and tumor cells reach the circulation through these new and permeable vessels. The vascular endothelial growth factor (VEGF) is the most prominent angiogenic growth factor. VEGF is produced by almost all solid tumors: its receptors are expressed only on vascular endothelial cells and predominantly in vessels in the proximity of the tumor. Therefore, the VEGF/VEGF-receptor system is a target for anti-angiogenic cancer therapy. Experiments show that inhibition of the VEGF-mediated endothelial cell activation interferes with tumor growth and metastases formation. Appropriate therapeutic strategies are currently under clinical investigation.