Modelling mesothelioma risk for workers assembling military gas masks

Our plain-English summary of Modelling mesothelioma risk for workers assembling military gas masks, by J.W. Cherrie, H.A. Cowie, A.D. Jones (Occupational and Environmental Medicine, 2007).

The study

• Authors: J.W. Cherrie, H.A. Cowie, A.D. Jones
• Journal: Occupational and Environmental Medicine
• Published: 2007;64(11):785-6; author reply 785-6
• Type of article: Comment, Letter
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Free full text

In plain English

This letter to the editor responded to an earlier study by McDonald and colleagues of a cohort of mostly women who made gas masks containing crocidolite asbestos between 1940 and 1944. Using a US Health Effects Institute risk model, the authors estimated mesothelioma deaths for a hypothetical group of women exposed to a high concentration of crocidolite for one year from age 20. The model was calibrated to the 65 mesotheliomas reported in that study. Without allowing for clearance of fibres from the lung or for deaths from other causes, predicted risk rose continuously. With clearance only (a half-time of 20 years), predicted deaths levelled off at about 1.8 per year. With competing deaths only, they peaked around 1990 and then fell rapidly. Combining both resembled the observed pattern, but it still predicted some mesothelioma deaths in the last eight years, when none had occurred. The authors suggested that the last survivors may have had the least exposure, or that lung cancer killed some highly exposed workers first. The authors concluded that risk methods lacking both clearance and competing deaths will overestimate risk, particularly for young people exposed.

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: Letter to the editor presenting a simplified mathematical modelling exercise, comparing model predictions with the mesothelioma data published by McDonald et al
• Who was studied: A hypothetical group of women exposed to a high concentration of crocidolite for one year starting at age 20. The model was calibrated to the 65 mesotheliomas reported by McDonald et al in their cohort of gas mask workers.
• Exposure: Crocidolite asbestos. The real cohort being modelled made gas masks incorporating crocidolite between 1940 and 1944. The model assumed one year of high-concentration exposure and a fibre clearance half-time of 20 years.
• Main results:
  • Without terms for fibre clearance or competing causes of death, the predicted mesothelioma risk in the modelled group increased continuously.
  • With only the clearance term, predicted deaths were much lower and tended to plateau at about 1.8 deaths per year.
  • With competing causes of death but no clearance, predicted deaths peaked in about 1990 (when the modelled women would have been 70) and then declined rapidly.
  • Combining clearance and competing causes of death gave a pattern similar to the observed data, but the model still predicted some mesothelioma deaths in the latter period of follow-up.
  • The elimination (clearance) factor reproduced the trend over the first eight periods but did not account for the lack of mesothelioma in the last eight years.
  • The authors suggested two possible explanations for the absence of mesothelioma deaths in the later periods. First, the final survivors may have been the least exposed workers. Second, lung cancer, with its shorter latency, may have killed some highly exposed people before mesothelioma did.
• The authors' conclusion: The authors concluded that asbestos risk assessments should account for both fibre clearance and death from other causes. In their view, methods that omit either term will overestimate risk, particularly for young people exposed to asbestos. They added that further research is needed on other processes affecting risk after very long follow-up.
• Limitations the authors state:
  • The model was simplified and relied on a few simplifying assumptions about a hypothetical group, not the actual workers.
  • The authors stated that it remains unknown whether other processes affect risk after very long follow-up.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite, Mesothelioma, Peritoneal mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma.

Related studies

• Sixty years on: the price of assembling military gas masks in 1940 — J.C. McDonald, J.M. Harris, et al. (2006)
• Lung fiber burden in the Nottingham gas mask cohort — G. Berry, F. Pooley, et al. (2009)
• Multistage modelling of lung cancer mortality in asbestos textile workers — N. Pearce (1988)
• Prediction modelling using routine clinical parameters to stratify survival in Malignant Pleural Mesothelioma patients undergoing cytoreductive surgery — E.J.A. Harris, S. Kao, et al. (2019)
• Mortality of two groups of women who manufactured gas masks from chrysotile and crocidolite asbestos: a 40-year follow-up — E.D. Acheson, M.J. Gardner, et al. (1982)
• Mesothelioma after crocidolite exposure during gas mask manufacture — A.D. McDonald, J.C. McDonald (1978)

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