May have an angiogenic function during early placental development. Binds to cell-surface heparan sulfate proteoglycans (HSPGs), and stimulates secretion of the proangiogenic factors VEGFA and TGFB from uterine dendritic cells and natural killer cells. Also induces endothelial tube formation in vitro. Expressed in placental trophoblast giant cells from 5.5 dpc onwards, with increased expression by 10.5 dpc (at protein level). Also detected on the decidua basalis at 10.5 dpc (at protein level). Belongs to the immunoglobulin superfamily. CEA family.