Mesothelioma is a rare form of cancer most commonly caused by exposure to asbestos. It develops from cells of the mesothelium, a protective lining that covers many of the internal organs of the body.
Asbestos was not mined and widely used commercially until the late 19th century. Its use was greatly increased during World War II. Since the early 1940s, millions of American workers have been exposed to the dust from this material. The risks associated with asbestos exposure were known shortly after its commercial introduction in the United States; however, the risks were not made public by the manufacturers.
An increased risk of developing mesothelioma was found among naval personnel (e.g., Navy, Marine Corps and Coast Guard). Shipyard workers, people who worked in asbestos mines and mills, producers of asbestos products, workers in the heating and construction industries were found to be at increased risk of developing this disease. The use of asbestos products in the automotive industry, and the production of many industrial products including cement, brake linings, gaskets, roof shingles, flooring products, textiles, and insulation has resulted in the exposure of asbestos dust to a tremendous number of tradespeople.
It has been recognized that the exposure to asbestos fibers is an occupational health hazard. Since the early 20th century, numerous epidemiological studies have associated occupational exposure to asbestos with the development of pleural plaques, diffuse pleural thickening, asbestosis, carcinoma of the lung and larynx, gastrointestinal tumors, and diffuse malignant mesothelioma of the pleura and peritoneum.
Family members and others living with asbestos workers also have an increased risk of developing mesothelioma and possibly other asbestos related diseases. This risk is likely the result of exposure to asbestos dust brought home on the clothing and hair of asbestos workers.
There is no evidence of a threshold level, below which there is no risk of mesothelioma. There appears to be no clear linear, dose-response relationship, with increasing dose producing increasing disease. Mesothelioma may be related to brief, low-level, or even indirect exposures to asbestos. The dose necessary for effect appears to be lower for asbestos-induced mesothelioma than for pulmonary asbestosis or lung cancer.
The official position of the U.S.Occupations Safety and Health Administration (OSHA) and the U.S. EPA is that protections and “permissible exposure limits” required by U.S. regulations, while adequate to prevent most asbestos-related non-malignant disease, are not adequate to prevent or protect against asbestos-related cancers such as mesothelioma.
The Health and Safety Executive of the British Government (HSE) states formally, “Any threshold for exposure to asbestos must be at a very low level, however, it is widely agreed that if any such threshold does exist at all, then it cannot currently be quantified”. For practical purposes, therefore, HSE assumes that no such “safe” threshold exists.
The time from first exposure to manifestation of disease is prolonged in the case of mesothelioma. It is virtually never less than fifteen years and peaks at 30–40 years. In a review of occupationally related mesothelioma cases, the median latency was 32 years.
Generally, a biopsy is needed to confirm a diagnosis of malignant mesothelioma.
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