Mesothelin is a 40kDa protein present on normal mesothelial cells and overexpressed in several human tumors, including mesothelioma and ovarian and pancreatic adenocarcinoma. The mesothelin gene encodes a precursor protein that is processed to yield mesothelin which is attached to the cell membrane by a glycosylphosphatidyl inositol linkage and a 31-kDa shed fragment named megakaryocyte-potentiating factor (MPF). Although it has been proposed that mesothelin is related to cell adhesion, its biological function is not known. Mesothelin has been proposed as a therapeutic target for cancer treatment.