Mesothelioma is an uncommon form of cancer, usually associated with previous exposure to asbestos, which affects the pleura, a sac which surrounds the lungs, the peritoneum, the lining of the abdominal cavity, or the pericardium, a sac that surrounds the heart.

In this disease, malignant (cancerous) cells are found in the mesothelium, a protective sac that covers most of the body's internal organs. Most people who develop mesothelioma have worked on jobs where they inhaled asbestos particles, or have been exposed to asbestos dust and fibre in other ways, such as by washing the clothes of a family member who worked with asbestos, or by home renovation using asbestos cement products.