20.12.2006 - Mesothelioma help and survival
There was one reported case of mesothelioma in a 62-year-old worker whose exposure to taconite had begun only 11 years before his death. Although latency periods as short as 15 years have been reported among insulation workers, mesothelioma generally occurs following a long latency period of 25 years or more (23). This person had previously been employed in the railroad industry, as a locomotive fireman and engineer, an occupational environment where both amosite and crocidolite asbestos insulation was used and opportunity for exposure existed (12). It is unlikely that this particular taconite exposure contributed to the appearance of mesothelioma.
Analysis of the mortality data, with a minimum latency period of 30 years, provided no evidence to support any association between exposure to quartz or elongated cleavage fragments of amphibole with lung cancer, nonmalignant respiratory disease, or any other specific disease.
Comparison of Occupational Cohorts Exposed to Iron Ore and Asbestos. The American and Canadian asbestos insulation workers are generally thought to have had exposure to the three principal commercial asbestos fiber typesgrunerite asbestos, crocidolite, and chrysotile (12). The tremolite asbestos in the vermiculite at Libby, Montana has never been extensively used in commerce in the United States. The vermiculite workers are an example of the effect of amphibole asbestos at concentrations of 1% in the ore. The mortality experience of the two asbestos-exposed groups are distinctly similar. Each shows an elevated risk of lung cancer, mesothelioma, and asbestosis (a nonmalignant respiratory disease). Of the 1,058 deaths reported in the most recent study of Minnesota taconite workers, one would have expected about 250 lung cancer (23.6%) and about 98 mesotheliomas (9.3%) if their mortality experience was similar to American and Canadian insulators (11). Instead, the actual number of lung cancer and mesotheliomas (Table 6) was 65 (6.1%) and 1 (0.09%), respectively.
Actually 32 fewer lung cancer occurred than the 97 expected (SMR = 67) using the rates for U.S. white males. The one mesothelioma that did occur had a latency of 11 years in taconite mining. In the large insulation cohort (17,800 workers), no mesothelioma was reported with a latency < 15 years, indicating the present case was unlikely to be related to his taconite dust exposure (11, 23). The mortality experience of the iron ore workers is, in fact, overall less than expected, indicating they are healthier than the general population. This healthy workers effect is commonly observed among many employed groups.
What are the risk factors for mesothelioma? Working with asbestos is the major risk factor for mesothelioma. A history of asbestos exposure at work is reported in about 70 percent to 80 percent of all cases. However, mesothelioma has been reported in some individuals without any known exposure to asbestos.
Asbestos is the name of a group of minerals that occur naturally as masses of strong, flexible fibers that can be separated into thin threads and woven. Asbestos has been widely used in many industrial products, including cement, brake linings, roof shingles, flooring products, textiles, and insulation. If tiny asbestos particles float in the air, especially during the manufacturing process, they may be inhaled or swallowed, and can cause serious health problems. In addition to mesothelioma, exposure to asbestos increases the risk of lung cancer, asbestosis (a noncancerous, chronic lung ailment), and other cancers, such as those of the larynx [The area of the throat containing the vocal cords and used for breathing, swallowing, and talking. Also called the voice box.] and kidney.
Smoking does not appear to increase the risk of mesothelioma. However, the combination of smoking and asbestos exposure significantly increases a person's risk of developing cancer of the air passageways in the lung.
5. Who is at increased risk for developing mesothelioma? Asbestos has been mined and used commercially since the late 1800s. Its use greatly increased during World War II. Since the early 1940s, millions of American workers have been exposed to asbestos dust. Initially, the risks associated with asbestos exposure were not known. However, an increased risk of developing mesothelioma was later found among shipyard workers, people who work in asbestos mines and mills, producers of asbestos products, workers in the heating and construction industries, and other tradespeople. Today, the U.S. Occupational Safety and Health Administration (OSHA) sets limits for acceptable levels of asbestos exposure in the workplace. People who work with asbestos wear personal protective equipment to lower their risk of exposure.
The risk of asbestos-related disease increases with heavier exposure to asbestos and longer exposure time. However, some individuals with only brief exposures have developed mesothelioma. On the other hand, not all workers who are heavily exposed develop asbestos-related diseases.
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