Asbestos Exposure - Mesothelioma, Lung Cancer, Fibrosis
In the second paper (McDonald et al., 1993), mortality up to the end of 1988 of the 5351 men who had survived into 1976 (of whom 16 could not be traced and 2827 had died) was followed. In this survivor population, the SMRs 20 or more years after first employment were 1.07 for all causes and 1.39 for lung cancer. The investigators subdivided the men into 10 groups based on cumulative exposure up to age 55. The highest relative risk (3.04) was in the highest exposure group (3 35 000 mpcm-years; 3 1000 mpcf-years), the second highest (1.65) was in the second highest exposure group (14 000 to 35 000 mpcm-years; 400 to 1000 mpcf-years) and the third highest (1.50) was in the third highest exposure group (10 500 to 14 000 mpcm-years; 300 to 400 mpcf-years). In the remaining 7 groups below 10 500 mpcm-years (300 mpcf-years), there was no indication of a trend or pattern of exposure-response with relative risks all being above 1 and averaging 1.27. Similar results were obtained in a heavily exposed subset of the cohort with a long duration of exposure (Nicholson et al., 1979). In the analysis of the large Quebec cohort, the relative increase in risk attributable to chrysotile exposure was lower for ex-smokers than smokers and negligible for smokers of 20 or more cigarettes a day. The authors concluded that the interaction appeared to be less than multiplicative.
The number of deaths attributed to mesothelioma in the Quebec cohort has increased with increasing age and time from first employment more rapidly than total mortality (McDonald et al., 1993). At the end of 1988, when some 75% of the cohort had died, and the youngest survivor was aged 73, in a total of 7312 male deaths, there were 33 suspected cases of mesothelioma, 15 coded to ICD 163 and 18 to a variety of other diagnostic codes. After review of all available evidence, including autopsies in 23 and biopsies in 10, the probability of the diagnosis being correct was assessed by the authors as high in 17, moderate in 11, and low in 5. All 33 cases were pleural but in one of low diagnostic probability, the peritoneum was also affected. Of the 33 cases, 20 were miners or millers from Thetford Mines, 8 were miners or millers from Asbestos, and the remaining five cases were observed among men employed in a small asbestos products factory in Asbestos. The median duration of employment was 36 years (range 2.5 to 49 years). There was no case of mesothelioma among the 4371 members of the cohort (40% of 10 925) employed for less than 2 years, eight cases among those 2396 (22%) employed for 2-10 years, and 25 mesotheliomas among the other 38% of the cohort (4158 men) with at least 10 years of employment. Crude rates of mesothelioma by cumulative exposure were calculated. Rates varied from 0.15 cases per 1000 man-years for those with exposures less than 3500 mpcm-years (100 mpcf-years) to 0.97 cases per 1000 man-years for those with exposure of 10 500 mpcm-years (300 mpcf-years) or more.
The most recent account of mortality among the chrysotile miners and millers of Balangero, Italy, was reported by Piolatto et al. (1990) for a cohort comprising 1094 men employed for at least one year between 1946 and 1987, with exposures estimated individually in fibre-years. Of the total, 36 could not be traced and 427 had died. The SMR for all causes based on national rates was 1.49, a high figure largely explained by hepatic cirrhosis and accidents. Numbers of deaths from all cancers (n=86) and lung cancer (n=22) were close to expected (76.2 and 19.9) and there was no evidence that the risk for either of these causes was related to duration of exposure, fibre-years of cumulative exposure, or time since first or last exposure. Little information was provided on the basis for the estimates of cumulative exposure. The first fibre counts were taken in 1969. Earlier exposure levels were estimated by simulating working situations occurring at various periods since 1946 in the plant, and fibre counts were measured by PCOM (Rubino et al., 1979b).
The cohort of chrysotile production workers employed at the Balangero mine and mill, studied by Piolatto et al. (1990), was almost exactly one tenth the size of the Quebec cohort. At the end of 1987, when 427 (45%) of the cohort had died, there were two deaths from pleural mesothelioma, both in men employed for more than 20 years, with cumulative exposure estimated respectively at 100-400 and > 400 f/ml years. One diagnosis was confirmed histopathologically, and one was based on radiological findings and examination of pleural fluid. Fibrous tremolite was not detected in samples of chrysotile from this mine, but another fibrous silicate (balangeroite), the biological effects of which are not known, was identified in low proportions by mass (0.2-0.5%). At a comparable stage in the evolution of the Quebec cohort, mesothelioma accounted for 10 out of 4547 deaths, a lower but not dissimilar proportion.
Mesothelioma Information
Malignant mesothelioma litigation is seen as peaking with 2,000 to 3,000 new cases of malignant mesothelioma cancer being diagnosed each year in the United States alone. An asbestos lawyer or mesothelioma attorney is able to track a case of malignant mesothelioma back to a source in order to help designate all liable parties.
Malignant Mesothelioma cancer is a latent disease that can take anywhere from 30 to 40 years to become fully developed. Once diagnosed, the average survival time is between one and two years. Mesothelioma treatment options have seen limited success in extending average survival rates, let alone containing the disease. Once mesothelioma symptoms begin to develop, it is typically too late for treatment to offer little more than palliative care.