Types of Mesothelioma - Asbestos Lung Cancer
b) Asbestos-cement production
Numerous studies have been conducted on asbestos-cement workers, but only four, analysing five factories, were of groups exposed almost only to chrysotile. In general, cumulative exposures were low, as were the observed SMRs. In the USA, Hughes et al. (1987) studied two asbestos-cement plants in Louisiana. Observed and expected deaths 20 years from onset of employment were provided according to exposure category. In plant 1, which dealt predominantly with chrysotile, small amounts of amosite were used from the early 1940s until the late 1960s and crocidolite for 10 years beginning in 1962. In plant 2, crocidolite was used continuously in the pipe department located in one building. Chrysotile was only used in the remaining three buildings, and lung cancer and mesothelioma mortality data were supplied for workers (63% of the total) whose only employment assignment was in these buildings. Cohort mortality analyses were conducted for both plant 1 and plant 2 workers 20 or more years after initial employment. There were 22 respiratory cancer deaths among 996 plant 1 employees with more than 6 months of service, which indicated a small non-significant lung cancer risk. However, a corresponding analysis of 42 lung cancer cases among 1414 plant 2 employees with more than 3 months of service and no assignment in the pipe building indicated a substantial lung cancer risk. Two deaths attributed to mesothelioma were reported among cohort members at plant 1 (mean exposure of 40 f/ml-years), while 1 death from mesothelioma was reported among workers at plant 2 (mean exposure of 19 f/ml-years).
Among 1176 Swedish asbestos-cement workers who were estimated to have used >99% chrysotile (Ohlson & Hogstedt, 1985), 11 cases of lung cancer were observed compared to 9 expected (9 observed versus 5.7 expected for those with a 20-year latency). This non-significant increase occurred in a plant with relatively low exposures. In a 10% sample of the work force, all employed for more than 10 years, overall cumulative exposure was 18 f/ml-years. Among the entire cohort, no deaths from mesothelioma were observed. In a study conducted in the United Kingdom (Gardner et al., 1986), the lack of lung cancer increase (35 observed versus 38 expected) can be explained by low cumulative exposures. Since 1970, mean levels were under 1 f/ml throughout the factory and most were under 0.5 f/ml. Higher concentrations of unknown magnitude would have existed prior to 1968. The possibility of low level smoking in the workforce compared to the general population masking lung cancer risks from chrysotile is considered unlikely by the authors. One death from mesothelioma (0.26% of total deaths) was reported among cohort members in this study. A study by Thomas et al. (1982) also did not indicate an excess lung cancer risk (30 observed versus 33.0 expected). Two deaths from mesothelioma (0.57% of all deaths) occurred in this cohort. As with the studies of Ohlson & Hogstedt (1985) and Gardner et al. (1986), the exposures in this plant were very low, the vast majority from 1972 to plant closure being consistently below 1 f/ml.
It must be noted, however, that in most of the cohort studies of asbestos-cement workers, there was no attempt to evaluate the most important confounder of lung cancer, i.e. smoking, or, alternatively, smoking rates were examined only for small subcohorts shortly before the end of follow-up.
(c) Textile manufacture
The health of employees has been studied in any detail in only three asbestos textile plants. These comprise a factory at Rochdale, England, originally studied by Doll (1955) and more recently by Peto et al. (1985), another located in Mannheim, Pennsylvania, USA, studied by McDonald et al. (1983b) and a plant in Charleston, South Carolina, USA. Only the study in South Carolina is considered primarily relevant for assessment of the health effects of chrysotile. Although the SMRs for lung cancer in these plants were broadly equivalent, the rates of mesothelioma varied considerably, which may reflect the greater proportions of amphiboles in the Mannheim and Rochdale cohorts.
The textile workers in the South Carolina plant have been studied in two separate but overlapping cohorts (Dement et al., 1983b; McDonald et al., 1983a; Brown et al., 1994; Dement et al., 1994). The only amphibole used in this plant was approximately one tonne of imported crocidolite from the early 1950s until 1972, plus a very small quantity of amosite for experimental purposes briefly in the late 1950s. The crocidolite yarn was processed at a single location only, so Charleston can be considered an almost pure chrysotile operation. Exposure levels for workers at this plant were estimated by Dementet al. (1983)
a) using nearly 6000 exposure measurements covering the period 1930-1975 and taking into account changes in plant processes and engineering controls (Table 7). The conversion of past exposures measured in mpcm (mpcf) to f/ml was based on both paired sample data (100 pairs) and concurrent samples (986 samples) by these two methods collected in plant operations during 1968-1971.
The most recent update of the Charleston study by Dement et al. (1994) demonstrated an overall lung cancer SMR of 1.97 (126 observed) and an overall SMR for non-malignant respiratory diseases (ICD 470-478 and 494-519) of 3.11 (69 observed). The data for white males, for which data were more complete, demonstrated an overall lung cancer SMR of 2.34 for those achieving at least 15 years of latency. The risk of lung cancer was found to increase rapidly in relation to cumulative exposure. Data for the entire cohort demonstrated an increase in the lung cancer risk of 2-3% for each fibre/ml-years of cumulative chrysotile exposure. Two mesotheliomas were observed among this cohort and an additional mesothelioma was identified among plant workers, occurred after the study follow-up period. Analyses of an overlapping cohort from the same factory (McDonald et al., 1983a) provided similar results.
It can be seen in Table 23 that the regression line slopes for relative risks of lung cancer in relation to accumulated exposure in the Charleston plant are all some 30 times steeper than those observed in chrysotile mining and cement product manufacture.
Mesothelioma Information
Malignant mesothelioma is a rare type of cancer that affects the serous membrane lining three of the body’s largest cavities. Therefore there are three distinct types of mesothelioma:
- Pleural mesothelioma
- Peritoneal mesothelioma
- Pericardial mesothelioma
Pleural mesothelioma is the most common type of the disease accounting for an approximate 75% of all documented cases. Because of its close proximity to the lungs, pleural mesothelioma is often misdiagnosed as a type of lung disease such as asbestos lung cancer or viral pneumonia.
Causes of mesothelioma have been limited to asbestos exposure, making asbestos product manufacturers liable for injuries incurred. Mesothelioma compensation is expected to exceed $200 billion when all is said and done.
If you or a loved one has been diagnosed with malignant mesothelioma or another type of asbestos-related disease, you may be eligible for compensation. Contact a mesothelioma attorney or asbestos lawyer to get more information about filing your asbestos lawsuit.