What is Mesothelioma? Mesothelioma is a cancer found in the lining surrounding the lungs, the stomach, the heart or the testicles. This cancer takes its name from the name that is given to this lining - the mesothelium. The pleura is the name for the mesothelial tissue surrounding the lungs and lining the chest cavity. If the cancer is in this lining, it is called "pleural mesothelioma." Pleural mesothelioma is the most common type of mesothelioma. The peritoneum is the lining that covers most of the organs in the abdominal cavity, while the pericardium is the lining that covers and protects the heart. If the cancer is in either of these areas, it is called "peritoneal mesothelioma" or "pericardial mesothelioma." Like other forms of cancer, mesothelioma occurs when cells become abnormal and divide or grow out of control. When someone has mesothelioma, the lubricating fluid in the lining may be over-produced. This excess fluid encases the or...