VEGF (vascular endothelial growth factor) is a homodimeric, disulfide-linked glycoprotein involved in angiogenesis which promotes tumor progression and metastasis. It exhibits potent mitogenic and permeability inducing properties specific for the vascular endothelium. Of the four isoforms of VEGF, the smaller two, VEGF165 and VEGF121, are secreted proteins and act as diffusible agents, whereas the larger two (VEGF189 and VEGF206) remain cell associated.