- Mesothelioma is a malignant tumor that affects the mesothelium, the protective lining of many internal organs, most commonly the lining of the lungs and chest cavity (pleura). - The vast majority of mesothelioma cases are linked to occupational or environmental exposure to asbestos fibers. - Cadmium, Arsenic, and Lead are heavy metals that are toxic and can cause various health problems, including other types of cancer (e.g., lung, bladder, skin for arsenic; lung, kidney, prostate for cadmium), but they are not the primary cause of mesothelioma.