Mesothelin is a glycosyl-phosphatidyl- inositol-anchored glycoprotein present on the cell surface of various human solid tumors. The mesothelin (MSLN) gene encodes a 71- kDa precursor protein that is processed to a 40- kDa glycosylphosphatidyl-inositol-anchored protein that composes the mature portion and an NH2-terminal 31- kDa fragment called megakaryocyte-potentiating factor that is released from the cell. Mesothelin is a tumor differentiation antigen present at low levels on a restricted set of normal adult tissues, such as mesothelium, but aberrantly over expressed in mesotheliomas, ovarian, and pancreatic cancers. The biological functions of mesothelin remain elusive. A recent study showed that mesothelin binds to MUC16/CA125, and that this interaction mediates cell adhesion, suggesting that there may be an important role for MUC16/CA125 and mesothelin in the metastatic spread of ovarian cancer.Synonyms: CAK1 antigen, MPF, MSLN, Pre-pro-megakaryocyte-potentiating factor