A mesothelioma is a benign or malignant tumor found in either the chest (75% are pleural, 2-3% pericardial) or abdomen (20% peritoneal, 1% scrotal). The word comes from “meso” (middle) and “epithelium” (covering/lining). Tumors develop when cells of the mesothelium (the middle layer of cells of the tissue) proliferate to cause abnormal thickening of the sack-like tissues found in the pleural, pericardial and peritoneal cavities.

There are 3 types of mesothelioma based on anatomical location (pleural, pericardial and peritoneal) and 3 sub-types of malignant mesotheliomas based on cell morphology (60% are epitheloid, 20% are sarcomatoid and about 25% are mixed). Sarcomatoid has the worst prognosis while epitheloid carries the best results.

Mesotheliomas are often discovered by finding excess fluid in the chest (chest x-ray), around the heart (echocardiography) and in the abdomen (ultrasound). Ultimately diagnosis comes from examination of mesothelial cells under the microscope. Treatment and prognosis are based on the type, sub-type and stage of the illness.