Malignant mesothelioma is a rare form of cancer that starts in the mesothelium, a membrane that covers and protects most internal organs of the body. The mesothelium has two layers, one surrounding the body itself, and the other forms a sac around it completely. A small amount of fluid is normally produced between these two layers, lubricating the movement of the protected. When normal cells of the mesothelium lose control and spread quickly, they produce mesothelioma. The form of mesothelioma is the most common mesothelioma "pleural". It occurs in the pleura, the lining of the lungs. Other forms are mesothelioma "peritoneal", reaching the peritoneum lining the abdominal cavity and mesothelioma "pericardial", pericardium, the lining of the heart.