MCAM (MUC18 antigen, CD146), a member of the immuoglobulin superfamily, is an intrinsic membrane glycoprotein of 110-120 kDa found on the surface of endothelial cells, bone marrow fibroblasts and various melanomas. MCAM (Melanoma adhesion molecule) has been used as a marker of tumor progression in human melanoma because expression in those tumors correlates strongly with poor prognosis and the development of metastic disease. In addition, a number of human T, B and myeloid leukemic cell lines seem to express MCAM. The close structural relationship with N-CAM and related molecules suggests that MCAM may be also a developmentally regulated cell adhesion.