CD146,also known as melanoma cell adhesion molecule (MCAM) or MUC18,originally identified as a biomarker of melanoma progression,is a transmembrane glycoprotein belonging to the immunoglobulin (Ig) superfamily . Structurally,it consists of five Ig domains,a transmembrane domain,and a cytoplasmic region. In normal adult tissue,CD146 is primarily expressed by vascular endothelium and smooth muscle. CD146 is a key cell adhesion protein in vascular endothelial cell activity and angiogenesis,and has been used as marker of circulating endothelium cells (CECs) .