The CD146 antigen, also known as melanoma cell adhesion molecule (MCAM) and MUC18, is an integral membrane glycoprotein belonging to the immunoglobulin superfamily. CD146 contains the characteristic immunoglobulin-like domains (V-V-C2-C2-C2), a transmembrane region, and a short cytoplasmic tail. The CD146 expression is detected in endothelial cells in vascular tissue throughout the body and plays a role in cell adhesion, as well as in cohesion of the endothelial monolayer at intercellular junctions in vascular tissue. As a Ca2+-independent cell adhesion molecule involved in heterophilic cell to cell interactions and a surface receptor, CD146 triggers tyrosine phosphorylation of FYN and PTK2 and subsequently induced signal transduction, proteolysis, or immune recognition. This protein is also expressed predominantly on metastatic lesions and advanced primary tumors, and thus has been suggested to play an important role in tumor progression and the development of metastasis in certain human carcinomas.