Asbestos– Occupational exposure to asbestos is the major causative factor for mesothelioma. Asbestos is the commercial name for a group of magnesium silicate fibrous minerals. It has been widely used in the building, shipping, and sound-proofing industries. Asbestos is made up of tiny bundles of fibers that may become airborne when asbestos- containing materials are damaged or disturbed. Mesothelioma occurs due to continued and prolong inhalation of these fibers. Most people who develop mesothelioma have a history of direct exposure to asbestos at the job. Some patients have been indirectly exposed, such as by washing the clothes of a family member who worked with asbestos or by home renovation using asbestos cement products. The lifetime risk of developing mesothelioma in heavily exposed individuals is as high as 7 to 10%. Symptoms of mesothelioma may not appear until 20 to 50 years after exposure to asbestos. The risk of developing mesothelioma increases over time, even after exposure to asbestos has been stopped.
It is important to note that some cases of mesothelioma have been reported in individuals without any known exposure to asbestos.
Whilst upto 90% of reported mesotheliomas are asbestos-related, other causative agents have been identified.
Radiation therapy– Radiation to chest or abdomen (used for treatment of other cancers) may be a risk factor for the subsequent development of mesothelioma. Usually, there is a long latent period between the initial treatment and the diagnosis of the mesothelioma.
Virus– Simian virus-40 (SV-40) is a virus with potential to cause cancers in humans. Some studies have shown the presence of this virus in a proportion of mesothelioma cases (some of which did not have obvious asbestos exposure). However, the causal nature of this association has been questioned and the exact role of simian virus 40 infection is unclear at present. An association between the simian virus 40 virus and mesothelioma could be exploited for early detection of tumor and treatment with potential vaccination.
Others– The development of malignant mesothelioma has also been associated in rare cases with exposure to Thorotrast, an X-ray contrast medium used in 1930-1950. Due to its side effects, the use of the contrast medium was banned and its production stopped in 1949/50.
Inhalation of erionite, a fibrous silicate mineral usually found in volcanic ash, has also been implicated in causation of this cancer. The mineral also has been found in gravel mines in southwestern North Dakota. Erionite is not currently regulated by the U.S. Environmental Protection Agency (EPA).