Mesothelioma is cancer of the mesothelium, a protective membrane that lines most of the body's internal organs. Three out of every four cases cases of mesothelioma disease begin in the pleural mesothelium of the chest cavity. Mesothelioma can also begin in the abdominal cavity and around the heart.
Regardless of where they originate, malignant cells from the mesothelium can invade and damage nearby tissues. Cancer cells can also metastasize, or spread, to other parts of the body.
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Often by the time mesothelioma is diagnosed, the disease is advanced. The five-year survival rate is around 5% to 10%. Most patients with mesothelioma die as a result of respiratory failure or pneumonia. Some patients develop a small-bowel obstruction when a tumor extends through the diaphragm. A smaller number die of cardiac complications when the tumor invades the pericardium -- the thin membrane that surrounds the heart -- and the heart itself.
Mesothelioma is a relatively rare form of cancer. About 3,000 new cases of the disease are diagnosed in the U.S. each year.
Causes of Mesothelioma
The main risk factor for mesothelioma is working with asbestos. Asbestos is a group of minerals with thin microscopic fibers. Because these fibers are resistant to heat, fire, and chemicals and do not conduct electricity, asbestos has been mined and used widely in the construction, automotive, and other industries.
If tiny asbestos fibers are released into the air, as they are in the manufacturing process, they can be inhaled or swallowed, leading to serious health problems. As many as 75% of mesothelioma cases can be linked to exposure to asbestos at work. There is also some evidence that family members and others living with asbestos workers have an increased risk of developing mesothelioma, and possibly other asbestos-related diseases. This risk may be the result of exposure to asbestos dust brought home on the clothing and hair of asbestos workers. Cases of mesothelioma have also been seen in people living close to asbestos mines.
However, mesothelioma has been reported in some individuals without any known exposure to asbestos. Other, uncommon, but possible causes include:
Zeolites. These minerals are chemically related to asbestos. One of these related minerals, erionite, is common in the soil in some areas of Turkey, according to the American Cancer Society. Exposure to erionite is believed to be responsible for high rates of mesothelioma rates in those areas.
Radiation: The American Cancer Society notes that there have been a few published reports of mesotheliomas that developed following exposure to high doses of radiation to the chest or abdomen or after injections of thorium dioxide (Thorotrast), a material used by doctors in some chest X-rays until the 1950s.
SV40 virus. Some studies in laboratory animals have raised the possibility that infection with the simian virus 40 (SV40) might increase the risk of developing mesothelioma, according to the American Cancer Society. Some injectable polio vaccines given between 1955 and 1963 were contaminated with SV40, exposing as many as 30 million people in the U.S. to the virus. So far, the largest studies addressing this issue in humans have not found an increased risk for mesothelioma or other cancers among people who received the contaminated vaccines as children.
Genetics. Some experts believe certain people may be genetically predisposed to mesothelioma. Rates of the disease vary among populations.