What is mesothelioma?

Mesothelioma is a rare form of cancer that arises in the mesothelium. The mesothelium is made up of visceral and parietal membranes (thin layers of tissue), which surround organs and body cavities, such as the lungs or abdomen. The visceral membrane immediately surrounds the organ, and the parietal membrane is a sac covering the visceral membrane. There is a lubricating fluid between these membranes that make up the mesothelium. This fluid helps organs move easily among surrounding structures. In the case of the lung, it helps reduce friction between the lung and chest wall during normal breathing as the lung expands. There are different types of mesothelioma, depending where it is found in the body. In the abdomen, it is called peritoneal mesothelioma; on the lungs, it is called pleural mesothelioma; and if it develops on the heart, pericardial mesothelioma.