Definition of Mesothelioma

Mesothelioma: A malignant tumor of the mesothelium. The mesothelium is the thin lining on the surface of the body cavities and the organs that are contained within them. Most mesotheliomas begin as one or more nodules that progressively grow to form a solid coating of tumor surrounding the lung, abdominal organs, or heart.

Mesothelioma most commonly occurs in the chest cavity and is associated with exposure to asbestos in up to 90% of cases. It has been shown that some asbestos fibers that are inhaled quickly work their way through the lung tissue and into the chest (pleural) cavity. Asbestos fibers that are swallowed have been shown to penetrate the wall of the intestine and appear in the abdominal (peritoneal) cavity.

The risk of mesothelioma increases with the intensity and duration of exposure to asbestos. It is debatable whether or not there is any safe exposure level. Mesothelioma typically does not occur for 20 to 50 years following exposure to asbestos. Some forms of asbestos, particularly crocidolite fibers, are more likely to cause mesotheliomas. There is also evidence that mesotheliomas may be caused by other agents including radiation, viruses, and man-made mineral fibers. There is no relationship to smoking.

Mesothelioma is currently difficult to treat in most cases and survival beyond two years is unusual.