There are two types of mesothelioma: 1. Pleural mesothelioma is a primary tumor of the pleura, which can be divided into localized (mostly benign) and diffuse (all malignant). Among them, diffuse malignant mesothelioma is one of the tumors with the worst prognosis in the chest. Most patients are between 40 and 70 years old, and there are more men than women. 2. Peritoneal mesothelioma refers to a tumor that originates in peritoneal mesothelial cells. The clinical manifestations are not characteristic, and common symptoms and signs include abdominal pain, ascites, abdominal distension, and abdominal masses. Peritoneal mesothelioma accounts for about 20% of all mesothelioma cases, and can occur in 2-92 years old, with an average age of 54 years old. About 63% of cases are between 45 and 64 years old, and children are rare.