CD105/Endoglin is a Type I membrane glycoprotein located on cell surfaces and is part of the TGF-beta receptor complex. This protein has been found on endothelial cells, activated macrophages, fibroblasts, and smooth-muscle cells. Endoglin has a role in the development of the cardiovascular system and in vascular remodeling. Its expression is regulated during heart development. CD105 is highly expressed in endothelial cells during tumor angiogenesis and inflammation, with weak or negative expression in vascular endothelium of normal tissues. Angiogenesis is a promising prognostic marker in a variety of tumors. Endoglin is a more specific and sensitive marker for tumor angiogenesis than CD31 or CD34, as it labels only newly-formed blood vessels and may serve as a prognostic marker for Prostate Adenocarcinoma, and cancers of the lung, stomach, breast, and brain.