Erc has been identified as a gene showing stronger expression in cancer-affected renal cell than in normal renal tissue in Eker rats (a rat model of renal cancer). The human homologue of the protein encoded by this gene is called MPF (megakaryocyte potentiating factor) or mesothelin. This protein is detected especially prominently in mesothelial cells, and its involvement has been suggested in the development of mesothelioma, making it a promising tumor marker. In humans, involvement of this protein has also been suggested in the development of pancreatic, ovarian and pulmonary cancers, etc. The protein is expressed as a GPI anchor-type membranous protein (about 71 kDa in molecular weight), which is thought to be digested by a furin-like protease to yield fragments about 31 kDa and 40 kDa in size. We have prepared an antibody specific to C-ERC/Mesothelin (40 kDa fragment).