Malignant mesothelioma is a rare form of cancer that is diagnosed in approximately 2,500 to 3,000 people each year. The disease usually affects the pleura, which is the membrane that lines the chest cavity and the lungs. It also may affect the peritoneum, which is the lining of the abdominal cavity.  Lastly in rare situations it can affect the pericardium, which is the lining around the heart.

People exposed to asbestos for a long time or exposed to high levels have an increased risk of developing malignant mesothelioma but even people exposed for a very short time can develop this disease. The disease occurs a minimum of 15 years (typically 20 to 40 years) after asbestos exposure. The average age at diagnosis is 50 to 70 years. More men than women are affected, probably because men are more likely to have worked in the industries that use asbestos.

Three main types of malignant mesothelioma are recognized: epithelial, sarcomatoid and mixed. The epithelial type is the most common.