Mesothelioma, more precisely malignant mesothelioma, is a rare form of cancer that develops from the protective lining that covers many of the body's internal organs, the mesothelium. It is usually caused by exposure to asbestos.
Mesothelioma most common site is the pleura (outer lining of the lungs and internal chest wall), but it may also occur in the peritoneum (the lining of the abdominal cavity), the pericardium (a sac that surrounds the heart), or the tunica vaginalis (a sac that surrounds the testis).
Most people who develop mesothelioma have worked on jobs where they inhaled asbestos, or they have been exposed to asbestos dust and fiber in other ways. It has also been suggested that washing the clothes of a family member who worked with asbestos can put a person at risk for developing mesothelioma.