VEGF (Vascular endothelial growth factor, VEGFA, VEGF-A), a dimeric ligand, is among the most potent angiogenic mitogens. VEGF is secreted by tumor cells and other cells exposed to hypoxia. VEGF is a highly specific mitogen for vascular endothelial cells. Seven VEGF isoforms (a, b, c, d, e, f, g) are generated as a result of alternative splicing from a single VEGF gene. All seven isoforms differ in their molecular mass and in biological properties such as their ability to bind to cell-surface heparan-sulfate proteoglycans. The expression of VEGF is potentiated and is secreted by tumor cells in response to hypoxia, by activated oncogenes, and by a variety of cytokines.