Mesothelioma risk after 40 years since first exposure to asbestos: a pooled analysis

Our plain-English summary of Mesothelioma risk after 40 years since first exposure to asbestos: a pooled analysis, by A. Reid, N.H. de Klerk, C. Magnani, et al (Thorax, 2014).

The study

• Authors: A. Reid, N.H. de Klerk, C. Magnani, D. Ferrante, G. Berry, A.W. Musk, E. Merler
• Journal: Thorax
• Published: 2014;69(9):843-50
• Cited by: 86 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The risk of malignant mesothelioma (MM) increases proportionally to the cumulative exposure, and to the 3rd or 4th power of time since first exposed, to asbestos. However, little is known about the risk of MM after more than 40 years since first exposure because most epidemiological studies do not have follow-up for sufficient periods of time.

Methods: The data from six cohort studies of exposed workers and two cohorts with residential exposure have been pooled. A nested case control design matched cases and controls on calendar period and age. Conditional logistic regression modelled the relationship between time since first exposure and risk of MM.

Results: The combined data consisted of 22,048 people with asbestos exposure (5769 women), 707 cases of pleural MM (165 in women) and 155 cases of peritoneal MM (32 in women). Median time since first exposure for pleural MM cases was 38.4 years (IQR 31.3-45.3). Median duration of exposure for pleural MM cases was 3.75 years (IQR 0.7-18.2). The rate and risk of pleural MM increased until 45 years following first exposure and then appeared to increase at a slower power of time since first exposure. The rate of increase in peritoneal MM over the 10-50 years since first exposure continued to increase.

Conclusions: Exposure to asbestos confers a long-term risk of developing pleural and peritoneal mesothelioma which increases following cessation of exposure. While the rate of increase appears to start to level out after 40-50 years no one survives long enough for the excess risk to disappear.

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In plain English

This pooled analysis combined six cohorts of asbestos workers with two cohorts exposed outside work. The worker cohorts were five in Italy (Eternit asbestos cement workers, amosite factory workers and three railway carriage workshop cohorts) and the Wittenoom crocidolite miners and millers in Australia. The other two were Wittenoom residents and wives of Eternit workers. Of 22,048 people (5769 women), 707 developed pleural and 155 peritoneal mesothelioma. Cases were compared with matched controls to see how risk changed with time since first exposure. Overall, 44% of pleural and 54% of peritoneal cases occurred 40 or more years after first exposure, and in women a larger share occurred after 40 years than in men. Pleural mesothelioma risk rose until about 45 years after first exposure and then tended to rise more slowly. Peritoneal risk kept rising with no sign of flattening. Mining and milling carried the greatest risk by source. The authors concluded that asbestos confers a long-term risk that increases after exposure ends, and that no one survives long enough for the risk to disappear.

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: Pooled analysis of eight cohort studies, analysed with a nested case-control design (cases matched to controls on calendar period and age) and conditional logistic regression
• Who was studied: 22,048 asbestos-exposed people (5769 women). Six occupational cohorts: in Italy, Eternit asbestos cement workers at Casale Monferrato, amosite factory workers at Molina di Ledro, and three railway carriage construction and maintenance cohorts; in Australia, Wittenoom crocidolite miners and millers. Two environmentally exposed cohorts: Wittenoom residents and wives of Eternit workers. Follow-up ran to the end of 2007 or 2008.
• Exposure: Wittenoom workers and residents were exposed only to crocidolite. Eternit workers and wives were exposed to a mixture, largely chrysotile and crocidolite. Railway stock workers were exposed predominantly to crocidolite and to chrysotile to a lesser extent. Amosite factory workers were exposed solely to amosite. Exposure was measured by time since first exposure and by duration of employment or residence. Median duration of exposure for pleural mesothelioma cases was 3.75 years.
• Main results:
  • There were 707 cases of pleural mesothelioma (542 in men) and 155 cases of peritoneal mesothelioma (123 in men) across all cohorts.
  • Across all cohorts, men and women together, 44% of pleural and 54% of peritoneal mesotheliomas occurred 40 years or more after first exposure.
  • Pleural mesothelioma occurring after 40 years since first exposure: 60% of cases in women compared with 40% in men.
  • 81% of peritoneal mesothelioma cases in women occurred more than 40 years after first exposure, compared with 47% in men.
  • The adjusted risk of pleural mesothelioma rose until about 45 years since first exposure, then tended to flatten, so that after 45 years the rate did not increase as quickly as a power of time since first exposure.
  • The adjusted risk of peritoneal mesothelioma rose in proportion to time since first exposure, with no evidence of flattening.
  • The time exponent (the power of time since first exposure) was 3.21 for peritoneal mesothelioma and 2.81 for pleural mesothelioma.
  • A fibre clearance term had an effect in the pleural model (minus 0.04) but no significant effect in the peritoneal model.
  • By source of exposure, mining and milling carried the greatest risk of both pleural and peritoneal mesothelioma.
  • Crocidolite carried the greatest risk of pleural mesothelioma compared with amosite and mixed fibres.
  • Risk was lower for women than for men.
  • The risk of peritoneal mesothelioma increased moderately with longer duration of exposure.
• The authors' conclusion: The authors concluded that asbestos exposure confers a long-term risk of pleural and peritoneal mesothelioma that keeps increasing after exposure stops, despite some fibre clearance. The rate of increase appears to level out for pleural mesothelioma after 40 to 50 years, but no one survives long enough for the risk to disappear.
• Limitations the authors state:
  • Mesothelioma is hard to diagnose and is often misclassified as lung cancer. With relatively few cases, any misclassification could substantially affect the results.
  • Cases identified only from death certificates did not undergo the same systematic diagnostic review as registry cases.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Wittenoom, Western Australia

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Meta-Analysis, Malignant Mesothelioma, Cumulative Exposure, Asbestos Exposure, Peritoneal Mesothelioma.

Related studies

• The risk of lung cancer with increasing time since ceasing exposure to asbestos and quitting smoking — A. Reid, N.H. de Klerk, et al. (2006)
• Malignant mesotheliomas in former miners and millers of crocidolite at Wittenoom (Western Australia) after more than 50 years follow-up — G. Berry, A. Reid, et al. (2012)
• Are children more vulnerable to mesothelioma than adults? A comparison of mesothelioma risk among children and adults exposed non-occupationally to blue asbestos at Wittenoom — A. Reid, P. Franklin, et al. (2018)
• Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom — A.W. Musk, N.H. de Klerk, et al. (2008)
• Exposures estimates of the Wittenoom mining workforce and town residents - Implications associated with risk estimation for persons exposed to asbestiform riebeckite — A.J. Rogers (2018)
• Cumulative asbestos exposure and mortality from asbestos related diseases in a pooled analysis of 21 asbestos cement cohorts in Italy — F. Luberto, D. Ferrante, et al. (2019)

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