Mesothelin is a glycoprotein weighing 40 kDa that is attached to the cell membrane by glycosyl-phosphatidylinositol. It is derived from a larger precursor protein of 71 kDa, which is generated by the human mesothelin gene. This protein is found on the exterior of normal mesothelial cells. Although its precise role remains unclear, mesothelin is produced in excess in many types of cancers, such as mesothelioma, pancreatic ductal adenocarcinoma, and ovarian carcinoma. This molecule has been recognized as an important marker for pancreatic ductal adenocarcinoma because it shows high reactivity in cancer tissue but is not found in healthy pancreatic cells. Metastatic renal cell carcinoma may exhibit symptoms similar to primary mesothelioma, pancreatic ductal adenocarcinoma, and ovarian carcinoma. Mesothelin has shown effectiveness in distinguishing these primary tumors from metastatic renal cell carcinoma when using an antibody panel for testing.