Mesothelioma is caused by long-term, repeated exposure to asbestos fibers. The disease is generally found in four different forms: pleural, peritoneal, pericardial, and testicular. In each case, the cancer develops in mesothelial cells, which form the membranous linings that surround and protect organs. The different names for each type of mesothelioma refer to the point of origin of the cancer. Mesothelial membranes are made up of two different layers, called the parietal and visceral layers. Parietal layers are outer layers, and these typically cover large areas such as the chest cavity (in the case of pleural and pericardial membranes) and the abdominal cavity (as in the case of peritoneal membranes). Visceral layers are those that cover organs such as the lungs and heart.




