Mesothelioma (cont.)

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The major known cause of mesothelioma is exposure to asbestos. A known history of asbestos exposure is present in a majority of cases of mesothelioma. Asbestos likely causes cancer by physically irritating the cells. When asbestos fibers are breathed in, they reach the ends of the small airways and penetrate into the pleura (lining of the lung). These fibers may then injure mesothelial cells of the pleura and eventually cause mesothelioma.

The risk of developing mesothelioma rises with the quantity of asbestos exposure. However, genetic factors also play a role in determining who develops the condition. This is probably the reason why all people exposed to high levels of asbestos do not develop mesothelioma.

Smoking

Although smoking has not been associated with the development of mesothelioma, the combination of smoking and asbestos exposure significantly increases a person's risk of developing lung cancer.

Mesothelioma also has been linked to the following:

• Radiation: Mesothelioma has been reported to occur in few people following exposure to therapeutic radiation using thorium dioxide (Thorotrast).
• Zeolite: Zeolite is a silicate mineral (chemically related to asbestos) commonly found in the soil of the Anatoli region of Turkey. A few cases of mesothelioma reported from this region may have been caused by zeolite.
• Simian virus 40 (SV40): The role of SV40 in the development of mesothelioma has also been suggested. This virus has been identified in human mesothelioma cells. In studies conducted in animals, it has been shown to induce the development of mesothelioma. In humans, the possibility of SV40 serving as a cofactor in the development of mesothelioma is inconclusive and further research is ongoing.