Risk of mesothelioma after cessation of asbestos exposure: a systematic review and meta-regression

Our plain-English summary of Risk of mesothelioma after cessation of asbestos exposure: a systematic review and meta-regression, by P. Boffetta, F. Donato, E. Pira, et al (International Archives of Occupational and Environmental Health, 2019).

The study

• Authors: P. Boffetta, F. Donato, E. Pira, H.N. Luu, C. La Vecchia
• Journal: International Archives of Occupational and Environmental Health
• Published: 2019;92(7):949-957
• Type of article: Meta-analysis, Systematic review
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Purpose: A 'risk reversal' has been observed for several human carcinogens following cessation of exposure, but it is unclear whether it also exists for asbestos-related mesothelioma.

Methods: We conducted a systematic review of the literature and identified nine studies that reported information on risk of mesothelioma after cessation of asbestos exposure, and performed a meta-regression based on random effects models. As comparison we analyzed results on lung cancer risk from four of these studies.

Results: A total of six risk estimates from five studies were included in the meta-analysis. The summary relative risk (RR) of mesothelioma for 10-year interval since cessation of exposure was 1.02 [95% confidence interval (CI) 0.87-1.19; p-heterogeneity 0.01]. The corresponding RR of lung cancer was 0.91 (95% CI 0.84-0.98).

Conclusions: This analysis provides evidence that the risk of mesothelioma does not decrease after cessation of asbestos exposure, while lung cancer risk does.

In plain English

This article was a systematic review and meta-regression of published studies on whether the risk of mesothelioma changes in the years after asbestos exposure stops. In April 2018 the authors searched PubMed and reference lists. They identified eight studies: seven industry-based studies of asbestos-exposed workers (in Italy, the UK, Germany, the USA and Poland) and one community-based case–control study from France. Most studies involved mixed or unspecified asbestos fibers. Six sets of results from five studies were pooled. For each additional 10 years since last exposure, the summary relative risk of mesothelioma was 1.02 (95% CI 0.87–1.19). The individual studies differed from one another more than chance would explain, and the data were too sparse to show why. In a comparison using four of the studies, the summary relative risk of lung cancer per 10 years was 0.91 (95% CI 0.84–0.98). The authors concluded that their results support the hypothesis that mesothelioma risk does not decrease after exposure stops. They noted several limitations: few studies were available, data 30 or more years after exposure stopped were sparse, leaving a job was assumed to mean exposure ended, and pleural and peritoneal cancer deaths were counted together with mesothelioma.

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: Systematic review and meta-regression (random-effects dose–response meta-analysis) of cohort and case–control studies
• Who was studied: Eight published studies reporting mesothelioma risk by time since last asbestos exposure. Seven were industry-based cohort or nested case–control studies from Italy, the UK, Germany, the USA and Poland. These included a UK survey of asbestos workers from mixed industries and German and Polish screening or surveillance programs. One was a community-based case–control study from France. Five studies, giving six sets of results, were included in the meta-regression.
• Exposure: Time since last occupational asbestos exposure. Most studies involved mixed or unspecified fibers. Individual studies covered asbestos cement workers (predominantly chrysotile), textile workers (amphibole, mainly crocidolite), pipe insulation workers (amosite) and chrysotile miners.
• Main results:
  • Across the pooled studies, the summary relative risk of mesothelioma per 10-year increase in time since last exposure was 1.02 (95% CI 0.87–1.19; p for heterogeneity 0.01).
  • The relative risks of the individual studies per 10-year increase in time since last exposure ranged from 0.60 to 1.36.
  • The data were too sparse to explain the differences between studies by characteristics of exposure (such as duration or asbestos type) or outcome.
  • For lung cancer, a comparable meta-regression of four studies gave a summary relative risk of 0.91 (95% CI 0.84–0.98; p for heterogeneity 0.42) per 10-year increase in time since last exposure.
  • Three studies were left out of the meta-regression because they did not report case, control or person-year numbers. The authors stated that the results of these three studies were consistent with their conclusion.
• The authors' conclusion: The authors concluded that their meta-analysis supports the hypothesis that mesothelioma risk does not decrease after asbestos exposure stops. They concluded that lung cancer risk does decrease.
• Limitations the authors state:
  • Few studies gave individual-level results, and results on mesothelioma arising three or more decades after exposure stopped were sparse.
  • The analysis assumed that leaving the job meant asbestos exposure ended. The authors said this kind of exposure misclassification would likely bias results toward the null.
  • Results for mesothelioma were combined with results for pleural and peritoneal cancer.
  • Results differed substantially between studies, and with so few studies the sources of these differences were hard to investigate.
  • The included studies adjusted for different sets of potential confounders.
  • Data on risk 30 or more years after exposure stopped were sparse, and the authors stated that no conclusions can be drawn for that period until more data accumulate.
  • The lung cancer comparison was restricted to the studies chosen for the mesothelioma review and was not based on its own systematic search.
  • Because most studies involved mixed or unspecified fibers, the authors could not assess whether the effect of stopping exposure differed by fiber type.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Asbestos Exposure, Systematic Review, Lung Cancer, Meta-Analysis, Relative Risk, confidence interval.

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