VEGFR-1 belongs to a family of five receptor tyrosine kinase receptors that are specific to a number of angiogenic factors including VEGF and PDGF, and are therefore thought to play a role in the angiogenic process. VEGFR-1 is expressed in two forms, predominantly on endothelial cells, giving rise to a full-length membrane bound receptor and a truncated soluble receptor. Elevated levels of the soluble form of this VEGF receptor may be used in the diagnosis of pathological conditions.