Plexin domain-containing protein 1, also known as tumor endothelial marker 3, tumor endothelial marker 7 and PLXDC1 and TEM3, is a secreted, cytoplasm and single-pass type I membrane protein which belongs to the plexin family. PLXDC1 / TEM3 is detected in endothelial cells from colorectal cancer, and in endothelial cells from primary cancers of the lung, liver, pancreas, breast and brain. It is expressed in fibrovascular membrane with increased expression in individuals with proliferative diabetic retinopathy. PLXDC1 / TEM3 is not detectable in endothelial cells from normal tissue. PLXDC1 / TEM3 plays a critical role in endothelial cell capillary morphogenesis. PLXDC1 / TEM3 may play a significant role in the proliferation and maintenance of neovascular endothelial cells in the formation of fibrovascular membranes (FVMs). PLXDC1 / TEM3 may be a molecular target for new diagnostic and therapeutic strategies for proliferative diabetic retinopathy (PDR). PLXDC1 / TEM3 interacts with NID1. It may also interact with CTTN.