Risk of mesothelioma and occupational exposure to asbestos and man-made vitreous fibers: evidence from two case-control studies in Montreal, Canada

Our plain-English summary of Risk of mesothelioma and occupational exposure to asbestos and man-made vitreous fibers: evidence from two case-control studies in Montreal, Canada, by J. Pintos, M.E. Parent, B.W. Case, et al (Journal of Occupational and Environmental Medicine, 2009).

The study

• Authors: J. Pintos, M.E. Parent, B.W. Case, M.C. Rousseau, J. Siemiatycki
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2009;51(10):1177-84
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To examine the effects of exposure to occupational asbestos and man-made vitreous fibers (MMVF) across a wide range of occupations on risk of mesothelioma.

Methodology: Two population-based case-control studies (1979-1986 and 1996-2001) provided 35 histologically confirmed mesothelioma cases and 1965 controls. A detailed job history was obtained to evaluate occupational exposure to many agents, including asbestos and MMVF.

Results: The mesothelioma odds ratio for exposure to any asbestos type was 3.7 (95% confidence interval = 1.7 to 7.8). The subset exposed to amphibole fibers experienced an odds ratio = 7.0 (95% confidence interval = 2.7 to 18.5). Effects of MMVF could not be disentangled from those of asbestos.

Discussion: In workers with exposure levels lower than in most historical cohort studies and across a wide range of industries, a strong association was found between asbestos, especially when it was amphibole, and mesothelioma.

In plain English

The authors pooled two population-based case-control studies from Montreal, Canada (1979–1986 and 1996–2001), comparing 35 men with malignant mesothelioma to 1,965 male controls. Chemists and industrial hygienists used each man's lifetime job history to judge exposure to asbestos (any fiber type, assumed to include chrysotile), amphibole asbestos, and man-made vitreous fibers (MMVF: glass and mineral wool fibers). Compared with men exposed to none of these fibers, the odds ratio for mesothelioma was 3.7 (95% confidence interval 1.7 to 7.8) for any asbestos exposure and 7.0 (2.7 to 18.5) for amphibole exposure. For substantial amphibole exposure it was 21.6 (5.1 to 90.3), based on 3 cases. The effects of MMVF could not be separated from those of asbestos. Unexpectedly, men exposed to both asbestos and MMVF had an odds ratio of 8.0 (3.4 to 18.9), versus 1.2 (0.3 to 4.3) for asbestos without MMVF. The authors concluded that asbestos, especially amphibole, was strongly associated with mesothelioma at exposure levels likely far below those in earlier studies. They noted wide, overlapping confidence intervals and a lack of quantitative exposure data.

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 two population-based case-control studies
• Who was studied: Men living in the Montreal area with histologically confirmed malignant mesothelioma identified in Montreal-area hospitals: 12 cases from study I (1979–1986, men aged 35 to 70) and 23 cases from study II (1996–2001, men and women aged 35 to 75, lung cancer or pleural mesothelioma), 35 in total. Controls were 1,965 men: 1,066 in study I (population controls from electoral lists plus a second set of cancer-patient controls) and 899 population controls in study II. Women were excluded from the results because few had these exposures.
• Exposure: Occupational exposure to asbestos (all fiber types, with all asbestos-exposed men assumed to have had chrysotile), amphibole asbestos (subtypes not distinguished), and man-made vitreous fibers (glass fibers and mineral wool fibers, grouped as MMVF). Exposure was judged by experts from interview-based lifetime job histories. 'Substantial' exposure meant medium or high concentration, more than 5% of the workweek, for 5 years or more.
• Main results:
  • Reference group: men not exposed to any of the fibers studied (18 cases, 1,502 controls).
  • Men ever exposed to asbestos of any type (15 cases, 337 controls): odds ratio 3.7 (95% CI 1.7 to 7.8), adjusted for age, ethnicity, schooling, smoking, respondent status and study.
  • Men with substantial exposure to asbestos of any type (3 cases, 36 controls): odds ratio 8.7 (95% CI 2.3 to 33.6).
  • Men ever exposed to amphibole fibers (7 cases, 115 controls): odds ratio 7.0 (95% CI 2.7 to 18.5).
  • Men with substantial exposure to amphibole fibers (3 cases, 15 controls): odds ratio 21.6 (95% CI 5.1 to 90.3). This was the highest odds ratio observed.
  • Men ever exposed to MMVF (11 cases, 171 controls): odds ratio 5.6 (95% CI 2.4 to 12.8). Asbestos and MMVF could not be included in the same models because of high collinearity, so the effects of MMVF could not be separated from those of asbestos.
  • Men exposed to both asbestos and MMVF (10 cases, 104 controls): odds ratio 8.0 (95% CI 3.4 to 18.9).
  • Men exposed to asbestos without MMVF (4 cases, 225 controls): odds ratio 1.2 (95% CI 0.3 to 4.3).
  • The authors described the higher risk in men exposed to both asbestos and MMVF, compared with asbestos alone, as unexpected.
  • The most common occupations among mesothelioma cases were in the construction industry, including electricians and pipefitters, and these occupations were more common among cases than among controls.
  • Less than half of the mesothelioma cases had suspected exposure to asbestos or MMVF.
• The authors' conclusion: The authors concluded that they found a strong association between exposure to asbestos, especially amphibole fibers, and mesothelioma, in populations exposed at levels they considered likely far below those studied previously. They also stated that they could not rule out a synergistic joint effect of MMVF and asbestos, and that their results on this point were inconclusive.
• Limitations the authors state:
  • Exposure misclassification was inevitable because there were no objective measurements. Exposures to chrysotile, amphiboles and MMVF were difficult to separate, and there were no quantitative data on exposure levels.
  • The authors could not confidently identify groups exposed only to amphiboles or only to chrysotile.
  • All asbestos-exposed men were assumed to have been exposed to chrysotile.
  • Confidence intervals were wide and overlapped considerably, so comparisons between the odds ratios call for caution.
  • The results may reflect some mutual confounding between asbestos and MMVF.
  • Too few men were exposed to MMVF without asbestos to analyze that group.
  • Exposure levels were probably much lower than in many historic cohort studies, which made effects harder to detect.

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, Occupational Exposure, Vitreous, Odds Ratio, confidence interval, Amphibole Group.

Related studies

• Occupational exposure to asbestos and man-made vitreous fibers, and risk of lung cancer: evidence from two case-control studies in Montreal, Canada — J. Pintos, M.E. Parent, et al. (2008)
• Lung cancer and exposure to man-made vitreous fibers: results from a pooled case-control study in Germany — H. Pohlabeln, K.H. Jöckel, et al. (2000)
• Man-made vitreous fibers and risk of respiratory system cancer: a review of the epidemiologic evidence — I.M. Lee, C.H. Hennekens, et al. (1995)
• Occupational exposure to asbestos and man-made vitreous fibres and risk of lung cancer: a multicentre case-control study in Europe — R. Carel, A.C. Olsson, et al. (2007)
• Cytotoxic and oxidative effects induced by man-made vitreous fibers (MMVFs) in a human mesothelial cell line — D. Cavallo, A. Campopiano, et al. (2004)
• Respiratory cancer and exposure to man-made vitreous fibers: a systematic review — D. Berrigan (2002)

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