Malignant mesothelioma is a rare cancer in which malignant or cancerous cells form in the thin layers of tissue lining the human chest, heart or abdomen. When the cancer is in the chest, it affects the pleura or tissue lining the lungs and is called malignant pleural mesothelioma. This is the most common type of mesothelioma. In the abdomen, a cancer of the peritoneum or tissue lining the abdominal cavity and covering various organs is called malignant peritoneal mesothelioma. The least common form of mesothelioma affects the pericardium, or outer lining of the heart. The term mesothelioma literally means a growth of the mesothelium, a layer of tissue from which the pleura, peritoneum and pericardium all develop.
