Mesothelin (MSLN) is a glycophosphatidylinositol (GPI)-linked cell surface protein normally expressed in mesothelial cells that line the pleura, peritoneum, and pericardium. The MSLN gene encodes a precursor protein of 71 kDa that is processed to a 31 kDa shed protein called MPF (megakaryocyte potentiating factor) and a 40 kDa membrane bound protein, mesothelin. Mesothelin is reported to be highly expressed in several types of malignant tumors, such as malignant mesothelioma, ovarian cancer, pancreatic adenocarcinoma, and lung adenocarcinoma.