Growth factor active in angiogenesis and endothelial cell growth, stimulating their proliferation and migration. It binds to the receptor FLT1/VEGFR-1. Also promotes cell tumor growth (By similarity). Antiparallel homodimer; disulfide-linked. Also found as heterodimer with VEGFA/VEGF (By similarity). Belongs to the PDGF/VEGF growth factor family.