CD146 (melanoma-associated antigen A32), also known as MUC18, is a transmembrane glycoprotein expressed on endothelial cells and is located at the intercellular junction where it plays a role in cell adhesion, and in the cohesion of the endothelial monolayer. CD146 labels endothelial cells, smooth muscle cells, intermediate trophoblast, subpopulation of T cells, and peripheral neuronal cells. In tumor, CD146 is expressed on tumor cells derived from the peripheral nervous system, melanoma and clear cell sarcoma. CD146 has been used as a marker for intermediate trophoblasts. It has been reported that CD146 is useful in differentiation of mesothelioma (CD146 positive) and reactive mesothelium (CD146 negative). CD146 is associated with tumor progression and the development of metastasis in human malignant melanoma.