Estimating the asbestos-related lung cancer burden from mesothelioma mortality

Our plain-English summary of Estimating the asbestos-related lung cancer burden from mesothelioma mortality, by V. McCormack, J. Peto, G. Byrnes, et al (British Journal of Cancer, 2012).

The study

• Authors: V. McCormack, J. Peto, G. Byrnes, K. Straif, P. Boffetta
• Journal: British Journal of Cancer
• Published: 2012;106(3):575-84
• Cited by: 71 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Quantifying the asbestos-related lung cancer burden is difficult in the presence of this disease's multiple causes. We explore two methods to estimate this burden using mesothelioma deaths as a proxy for asbestos exposure.

Methods: From the follow-up of 55 asbestos cohorts, we estimated ratios of (i) absolute number of asbestos-related lung cancers to mesothelioma deaths; (ii) excess lung cancer relative risk (%) to mesothelioma mortality per 1000 non-asbestos-related deaths.

Results: Ratios varied by asbestos type; there were a mean 0.7 (95% confidence interval 0.5, 1.0) asbestos-related lung cancers per mesothelioma death in crocidolite cohorts (n=6 estimates), 6.1 (3.6, 10.5) in chrysotile (n=16), 4.0 (2.8, 5.9) in amosite (n=4) and 1.9 (1.4, 2.6) in mixed asbestos fibre cohorts (n=31). In a population with 2 mesothelioma deaths per 1000 deaths at ages 40-84 years (e.g., US men), the estimated lung cancer population attributable fraction due to mixed asbestos was estimated to be 4.0%.

Conclusion: All types of asbestos fibres kill at least twice as many people through lung cancer than through mesothelioma, except for crocidolite. For chrysotile, widely consumed today, asbestos-related lung cancers cannot be robustly estimated from few mesothelioma deaths and the latter cannot be used to infer no excess risk of lung or other cancers.

In plain English

This study pooled published studies of asbestos-exposed workers to estimate asbestos-related lung cancer deaths per mesothelioma death. It combined 55 publications giving 68 estimates, mostly from North America and Europe. They estimated an average of 0.7 (95% CI 0.5 to 1.0) asbestos-related lung cancer deaths per mesothelioma death for crocidolite, 6.1 (3.6 to 10.5) for chrysotile, 4.0 (2.8 to 5.9) for amosite and 1.9 (1.4 to 2.6) for mixed fibers. The chrysotile figure was imprecise because mesothelioma deaths were few; four cohorts had none. Lung cancer figures in 78% of cohorts were not adjusted for smoking. Applying the mixed-fiber ratios to US men aged 40 to 84 in 2001 to 2005, the authors estimated that 3.2% to 4.0% (first method) or 4.3% to 5.4% (second method) of lung cancer deaths were due to asbestos. In each range the lower figure used smoking-corrected ratios, which the authors considered a lower limit. The authors concluded that for every asbestos type except crocidolite, asbestos-related lung cancer deaths outnumber mesothelioma deaths. They also concluded that few mesotheliomas after chrysotile exposure do not imply a small lung cancer burden.

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: Meta-analysis of published cohort studies of asbestos-exposed workers, estimating ratios of asbestos-related lung cancer deaths to mesothelioma deaths
• Who was studied: 55 published cohorts of asbestos-exposed workers (68 estimates), identified by a PubMed search last updated 1 September 2011, mostly from North America and Europe. The ratios were then applied to men aged 40 to 84 in 20 countries for 2001 to 2005, using WHO mortality data.
• Exposure: Occupational asbestos exposure grouped by fiber type: crocidolite, crocidolite plus chrysotile, predominantly chrysotile, amosite, and mixed or unspecified fibers. The authors also included one anthophyllite cohort and one vermiculite (tremolite-containing) cohort.
• Main results:
  • Crocidolite cohorts: mean 0.7 (95% CI 0.5, 1.0) asbestos-related lung cancers per mesothelioma death
  • Cohorts exposed to chrysotile with some crocidolite: overall estimate of 1.44 excess lung cancers per mesothelioma death
  • Chrysotile cohorts (16 estimates): mean 6.1 (95% CI 3.6, 10.5) excess lung cancers per mesothelioma death
  • The chrysotile estimates were large but imprecise because mesothelioma deaths were few; four chrysotile cohorts had no mesothelioma deaths
  • Amosite cohorts (4 estimates): mean 4.0 (95% CI 2.8, 5.9) excess lung cancers per mesothelioma death
  • All mixed-fiber cohorts combined: 1.9 (95% CI 1.4, 2.6) excess lung cancer deaths per mesothelioma death, with large heterogeneity
  • Lung cancer SMRs in 78% of the included cohorts were not adjusted for smoking
  • US men, mixed asbestos: estimated population attributable fraction of lung cancer of 3.2% to 4.0% using the first ratio method (R1)
  • US men, mixed asbestos: Table 4 gives 4.3% to 5.4% using the second ratio method (R2)
  • In Table 4, the lower end of each mixed-fiber range uses ratios corrected for smoking (R1 1.5, R2 2.2) and the upper end uses uncorrected ratios (R1 1.9, R2 2.8). The authors said the smoking-corrected estimates can be considered a lower limit.
  • Australian men: using the crocidolite ratios, an estimated 5.4% to 8.6% of lung cancer deaths were asbestos-related
• The authors' conclusion: The authors concluded that for all asbestos types other than crocidolite, asbestos-related lung cancer deaths outnumber mesothelioma deaths. They also concluded that few mesotheliomas after chrysotile exposure cannot be used to imply a small asbestos-related lung cancer burden.
• Limitations the authors state:
  • The effect of factors other than fiber type (such as dose, length of follow-up and exposure intensity) could not be examined for lack of data
  • Many mesotheliomas in chrysotile cohorts may actually be due to amphibole exposure
  • Inaccurate death certificate recording may have overestimated the ratios
  • The smoking correction applied is likely exaggerated and may underestimate the ratios and attributable fractions
  • Exposures in the general population may differ from those in the cohorts, and the largest exposed groups may not be represented in them

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: Lung Cancer, Mesothelioma, Asbestos Exposure, Relative Risk, confidence interval, Crocidolite, Chrysotile, Amosite.

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