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Mesothelioma causes |
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Asbestos exposure - the main mesothelioma cause Many epidemiologic surveys around the world have revealed prior exposure o asbestos in about 70-80% of all cases of mesothelioma. After 15 years of exposure to asbestos, 6% of the workers over 35 have died of mesothelioma. The death rate from mesothelioma in a group of asbestos workers was 344 times higher than in the general population. It is estimated that from 1940 through 1980 approximately 27,5 million workers were expose to asbestos in United States. With the calculated annual death rate from mesothelioma of about 2000 in 1980 up to 3000 in the late 1990` s . Corporations that manufacture asbestos products have known about the dangers of asbestos-related diseases for more than six decades. In an effort to increase profit, they kept this information quiet, putting workers and families at risk. Not only occupational exposure but also environmental, or even familial by household contamination is responsible for mesothelioma. The latter type of exposure usually through the work clothes of an asbestos worker is an important factor for woman. The delay between first exposure and onset of the disease is extremely long averaging 35-40 years with a usual range of 10-65 years. Because of such a delay, asbestos exposure can easily be underestimated since occupational histories are often inadequately documented. Moreover, exposure may have been minimal/short, although sometimes a very short exposure may have been intense. The asbestos minerals are divided into two major categories: the serpentines ( crysotile ), forming long hollow tubes, and the amphiboles containing more silica and less magnesium oxide and forming short straight fibers. Among the various types of asbestos associated with mesothelioma, amphiboles carry the highest risk. Crysotile, a long curly fiber with poor pulmonary penetration and which can be dissolved in lung tissue, seems to carry a much lower risk, although it does not appear to be nil. It has been postulated that mesotheliomas accurring in crysotile expose individuals my be related to contamination by tremolite, another amphibole fiber which has been implicated in cases of mesothelioma in Greece, and which make contaminated other substances such as talc or vermiculite. On the other hand, another amphibole fiber mined in Finland anthophyllite, a thick coarse fiber has been shown to cause calcified pleural plaques but not mesothelioma. This data emphasize the importance of the type of fiber and its physical characteristics, realizing also that most natural asbestos fibers are rarely pure but mixed. Mesothelioma: experimental evidence for the role of asbestos Animal experiments have confirmed the oncogenicity of asbestos. A single intrapleural or intraperitoneal injection of various asbestos fibers ( crysotile or amphiboles) produce mesotheliomas in rats, hamsters and mice, often after a relatively long delay of seven month or more. Read it all
Other causes of mesothelioma Since about 20% of patients have no demonstrable nor anamnestic exposure to asbestos, and some have an asbestos lung burden similar to controls, other factors are presumably involved. Other etiologic factors are rarely found, however the role of different fibers such as zeolites (crionite type) from volcanic rocs has been incriminated in Turkey and few deposits have been found in Oregon in the United States. The potential of zeolites to produce mesotheliomas has been confirmed experimentally after intraperitoneal injection. After inhalation the mesothelioma yield from zeolites exceeds that of any other fibers. Workers in the fiberglass industry are under close surveillance but so far there is no evidence that they have a higher risk of cancer or mesothelioma. Mesotheliomas have occurred within or in proximity of prior radiotherapy fields. In a cumulative review of nine cases of possible radiation induced mesothelioma, including two after extravasation of thorium dioxide the interval between radiation and mesothelioma ranged from 7-36 years, with a medium of 18 years. Radiation has also been shown to induce mesothelioma in animals. A few cases of mesothelioma have been described 15-33 years following collapsotherapy (the induction of an artificial pneumothorax), for tuberculosis, a technique used before effective drugs were available. Simian Virus 40 (SV40) - this virus has recently been identified by researchers in human mesothelioma cells, and has been shown to induce mesothelioma in the animal model. Polio vaccines administered as a primary prevention measure during 1955 - 1961 have been shown to be contaminated with SV40. However the implications of these facts are not totally understood and further research will be needed to clarify the link between malignant mesothelioma and a viral etiology.Although tobacco smoking has not been associated with the development of mesothelioma, the combination of smoking and asbestos exposure greatly increases the risk of lung cancer. Asbestos workers who also smoke have a lung cancer risk 50 to 90 times greater than that of the general population. More asbestos workers die of lung cancer than of mesothelioma. It is speculated that chronic irritation and inflammation may play a role in such cases. A similar mechanism has been postulated in a patient without known asbestos exposure who developed peritoneal mesothelioma associated with severe persistent diverticulitis and peritonitis, who showed histologic evidence of benign mesothelial proliferation and malignant mesothelioma. A case of peritoneal mesothelioma has also been reported in a patient with familial Mediterranean Fever with recurrent peritonitis. Two observed associations with mesothelioma are of importance. Various imunoproliferative disorders particularly of B cell origin, have been reported, including myolome, plasmocytome, limphocytic lymphoma and chronic lymphocytic leukemia in patients with asbestosis or mesothelioma. A case-control study showed an association between occupational exposure to asbestos and large cell lymphomas of the gastroinestinal tract and oral cavity. Asbestos fibers can disseminated by lymphatic and even hematogenous routes, and can be found in various organs included lymph notes and bone-marrow. Clinical observation also strongly suggest a genetic susceptibility to mesothelioma. Clusters of cases have been reported in some families, often by household exposure to asbestos, and also in identical twins. Sponsor:
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