Vascular endothelial growth factor D (VEGF-D), also known as c-fos-induced growth factor (FIGF), is a member of the VEGF family. VEGF-D is structurally similar to VEGF-C and both are specific ligands for the tyrosine kinase receptor VEGFR-3 (flt-4). They are both secreted as non-covalent homodimers. The secreted VEGF-D undergoes a complex proteolytic process enabling it to also act as a ligand for VEGFR-2 (KDR/flk-1). VEGF-D is expressed in adult lungs, heart, muscles, and small intestines. It is most abundantly expressed in the fetal lungs and skin. VEGF-D exhibits mitogenic effects on vascular and lymphatic endothelial cells. VEGF-D functions in the formation of the venous and lymphatic vascular systems during embryogenesis and in the maintenance of differentiated lymphatic endothelium in adults. Both VEGF-C and VEGF-D are over-expressed in certain cancers and promote tumor lymphangiogenesis. TGF-β1 has been shown to downregulate VEGF-D expression in human lung fibroblasts.