Mesothelioma is a very rare form of lung cancer that arises in the mesothelium. Mesothelioma research clinics indicate that Malignant mesothelioma is caused by asbestos exposure. Once malignant mesothelioma is found, more tests will be done to find out if cancer cells have spread to other parts of the body. The most common type of mesothelioma is pleural mesothelioma.