Prediction of mesothelioma and lung cancer in a cohort of asbestos exposed workers

Our plain-English summary of Prediction of mesothelioma and lung cancer in a cohort of asbestos exposed workers, by A. Gasparrini, A.M. Pizzo, G. Gorini, et al (European Journal of Epidemiology, 2008).

The study

• Authors: A. Gasparrini, A.M. Pizzo, G. Gorini, A. Seniori Costantini, S. Silvestri, C. Ciapini, A. Innocenti, G. Berry
• Journal: European Journal of Epidemiology
• Published: 2008;23(8):541-6
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Several papers have reported state-wide projections of mesothelioma deaths, but few have computed these predictions in selected exposed groups.

Objective: To predict the future deaths attributable to asbestos in a cohort of railway rolling stock workers.

Methods: The future mortality of the 1,146 living workers has been computed in term of individual probability of dying for three different risks: baseline mortality, lung cancer excess, mesothelioma mortality. Lung cancer mortality attributable to asbestos was calculated assuming the excess risk as stable or with a decrease after a period of time since first exposure. Mesothelioma mortality was based on cumulative exposure and time since first exposure, with the inclusion of a term for clearance of asbestos fibres from the lung.

Results: The most likely range of the number of deaths attributable to asbestos in the period 2005-2050 was 15-30 for excess of lung cancer, and 23-35 for mesothelioma.

Conclusion: This study provides predictions of asbestos-related mortality even in a selected cohort of exposed subjects, using previous knowledge about exposure-response relationship. The inclusion of individual information in the projection model helps reduce misclassification and improves the results. The method could be extended in other selected cohorts.

In plain English

The authors studied 2,246 male blue-collar workers at Breda, a railway rolling stock factory in Pistoia, Italy, that used asbestos from the late 1950s to the early 1980s. Sprayed asbestos insulation (crocidolite for at least 15 years, then amosite and chrysotile) ran until 1979. Follow-up from 1960 to 2004 recorded 1,080 deaths. Against Tuscany population rates, excluding the first 10 years after first exposure, lung cancer deaths were raised (132 cases; SMR 1.36, 95% CI 1.14–1.61), as were mesothelioma deaths (16 cases; SMR 8.65, 95% CI 4.94–14.05). Mesothelioma rose with duration of exposure; lung cancer did not. Models predicted deaths among the 1,146 workers alive at the end of 2004. For 2005–2050 they predicted 23.2 to 34.6 mesothelioma deaths and 14.8 to 29.7 excess lung cancer deaths. This depended on assumed lung fiber clearance (5% or 15% a year) and whether the asbestos-related lung cancer excess stayed stable or fell 5% yearly after 35 years from first exposure. The authors concluded that credible predictions were possible even with few cases, while noting several assumptions and no measure of uncertainty.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cohort mortality analysis followed by modelled predictions of future deaths attributable to asbestos (2005–2050), using individual probabilities of dying
• Who was studied: 2,246 male blue-collar workers at the Breda railway rolling stock factory, Pistoia, Tuscany, Italy, who were working there on 1 January 1960 or were hired before 31 December 1979 and worked at least 1 month. They were followed from 1960 to 2004. Predictions covered the 1,146 still alive at 31 December 2004 (mean age 64.7 years).
• Exposure: The factory used asbestos from the end of the 1950s to the beginning of the 1980s. The main route was sprayed asbestos insulation of railway coaches: crocidolite for at least 15 years, followed by amosite and chrysotile in the last period. Sprayed asbestos was used until 1979. The spraying itself was done by contract workers who were not in the cohort. Breda workers were exposed through assembly work that disturbed the asbestos layer, and through sprayed amosite roof insulation in 1974. Estimated intensity was 0.01 to 3.12 fibres/cc. Duration of exposure was used as a proxy for cumulative dose.
• Main results:
  • Over follow-up, 1,080 deaths occurred in the cohort, including 134 from lung cancer and 16 from mesothelioma.
  • Excluding the first 10 years after first exposure, lung cancer deaths in the cohort were raised compared with the Tuscany population: 132 cases, SMR 1.36 (95% CI 1.14–1.61).
  • Mesothelioma deaths (coded as pleural cancer) were raised in the cohort: 16 cases, SMR 8.65 (95% CI 4.94–14.05).
  • Excluding deaths from the excess of these two cancers, overall mortality in the cohort did not differ from expected (SMR 0.98, 95% CI 0.92–1.04).
  • Mesothelioma was strongly related to both duration of exposure and time since first exposure. Only 2 of the 16 deaths occurred in workers with less than 10 years of exposure. The SMR ratio between workers with more than and less than 10 years of exposure was about 3.3. Lung cancer showed no effect of duration of exposure.
  • Predicted mesothelioma deaths for 2005–2050 among the 1,146 living workers were 34.6 (assuming 5% annual fiber elimination) and 23.2 (assuming 15%).
  • Predicted excess lung cancer deaths for 2005–2050 were 29.7 with no decline in the excess risk and 14.8 with a 5% annual decline in the excess after 35 years since first exposure. The models indicated that the peak number of deaths had already been reached.
  • In a sensitivity analysis limited to workers with more than 10 years of exposure, the models predicted 18.5 and 12.1 mesothelioma deaths (5% and 15% elimination rates) and 3.7 to 9.2 excess lung cancer deaths.
• The authors' conclusion: The authors concluded that credible predictions of asbestos-related mortality can be computed even with a small number of cases, using a simple model and prior knowledge of the exposure-response relationship. They also concluded that individual information reduces misclassification and that the method could be extended to other selected cohorts.
• Limitations the authors state:
  • The predictions rest on several assumptions and include no measure of uncertainty.
  • Individual cumulative exposure could not be assigned, so duration of exposure was used as a proxy.
  • Because there were few cases, the four mesothelioma model parameters could not all be estimated. The lag time and the fiber elimination rate were taken from the literature.
  • The estimate of the mesothelioma SMR ratio by duration of exposure was highly uncertain.
  • Future baseline mortality was computed from 2000–2004 rates. If those rates fall, asbestos-related deaths could be higher than predicted.
  • Lung cancer rates are likely to fall as smoking declines in Italy, so the predicted excess may be slightly overestimated.
  • Reduced exposure in the 1970s may not yet show in mesothelioma deaths, so the estimated parameters might not apply to future years.
  • Every worker was assigned the same lung cancer risk, and this model could be too simple.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Lung Cancer, Cumulative Exposure.

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• Predictions of mortality from pleural mesothelioma in Italy: a model based on asbestos consumption figures supports results from age-period-cohort models — A. Marinaccio, F. Montanaro, et al. (2005)
• Lung function predicts mortality: 10-year follow-up after lung cancer screening among asbestos-exposed workers — T. Vehmas, P. Pallasaho, et al. (2013)
• A cohort study on mortality among wives of workers in the asbestos cement industry in Casale Monferrato, Italy — C. Magnani, B. Terracini, et al. (1993)

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