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. In humans, Endoglin may be involved in the autosomal dominant disorder known as Hereditary Hemorrhagic Telangiectasia Type 1. 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 controlled by angiogenic factors, mostly secreted by tumor cells. Vascular Endothelial Growth Factor (VEGF) is a potent angiogenic growth factor that stimulates endothelial cell proliferation and induces microvessel permeability. Studies have demonstrated a correlation between VEGF expression and vascular density. Angiogenesis has been proposed as a promising prognostic marker in a variety of tumors. Most studies of angiogenesis have been done with pan-endothelial markers such as CD31 or CD34. Endoglin is a more specific and sensitive marker for tumor angiogenesis than CD31, 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. CD105 may serve as a target for anti-angiogenesis therapy.