Mesotheliomas are tumors that arise in the pleural or peritoneal mesothelium as a result of exposure to asbestos. Mesothelium is a membrane that lines and lubricates body cavities. Mesothelioma arises when these cells become abnormal and divide uncontrolled. Pleural tumors compromise about 80% of mesotheliomas, whereas peritoneal tumors occur in 20% of cases. There are two distinct types of pleural mesotheliomas; diffuse, which are usually malignant, and localized, which are mostly benign.

There is a 3:1 male to female ratio and there is an 8% lifetime risk of developing the disease. Asbestos exposure usually occurs more than 20 years before the development of the disease. About 75% of patients with malignant mesothelioma have a know exposure to asbestos. Exposure may occur in the mining, milling, building and demolition, and automobile industries, which use asbestos products. There are about 2500-3000 new cases reported each year.

Cigarette smoking is known to exacerbate those with asbestosis, however there is no link between smoking and the development of mesothelioma.