Mesothelin, also known as CAK1 and ERC, is derived from a precursor that also includes Megakaryocyte Potentiating Factor (MPF). Following cleavage of the precursor, Mesothelin remains attached to the cell surface via a GPI linkage. Mesothelin is normally expressed on mesothelial cells in the pleura, pericardium, and peritoneum as well as in the developing and postnatal pancreas. It is upregulated in mesotheliomas and a range of carcinomas and adenomas. Mesothelin promotes tumor cell proliferation, migration, anchorage-independent growth, and tumor progression.