Mesothelioma risk among those exposed to chrysotile asbestos only and mixtures that include amphibole: a case-control study in the USA, 1975-1980

Our plain-English summary of Mesothelioma risk among those exposed to chrysotile asbestos only and mixtures that include amphibole: a case-control study in the USA, 1975-1980, by J.Y.Y. Wong, C. Rice, A. Blair, et al (Occupational and Environmental Medicine, 2021).

The study

• Authors: J.Y.Y. Wong, C. Rice, A. Blair, D.T. Silverman
• Journal: Occupational and Environmental Medicine
• Published: 2021;78(3):199-202
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: Occupational asbestos exposure is causally linked to mesothelioma. However, whether exposure to only chrysotile asbestos is associated with mesothelioma risk, and the heterogeneity in risk by different fibre types/lengths remains unclear. We investigated whether mesothelioma risk differs among workers exposed to only chrysotile asbestos compared with chrysotile and ≥1 amphibole (ie, amosite, tremolite, anthophyllite and crocidolite) over the working lifetime.

Methods: We analysed next-of-kin interview data including occupational histories for 580 white men (176 cases and 404 controls) from a case-control study of mesothelioma conducted in the USA in 1975-1980. Asbestos exposure was determined by an occupational hygienist using a job-exposure matrix and exposure categories included chrysotile only and nine chrysotile-amphibole mixtures. Logistic regression models were used to estimate the ORs and 95% CIs of mesothelioma, comparing each asbestos category to the unexposed group, adjusted for age at death and data source. Analysis of contrasts was used to assess overall heterogeneity and pair-wise differences in risk.

Results: Exposure to long and short chrysotile only was associated with increased mesothelioma risk compared with the unexposed (OR=3.8 (95% CI 1.3 to 11.2)). The complex mixture of extra-long amosite, short and long chrysotile, tremolite and anthophyllite was associated with the highest risk (OR=12.8 (95% CI 4.1 to 40.2)). There was evidence for overall heterogeneity among the asbestos exposure categories (p heterogeneity=0.02). However, the lower risk observed for exposure to chrysotile only compared with the complex mixture was not significant (p difference=0.10).

Conclusions: Our findings suggest that policies aimed at regulating asbestos should target both pure chrysotile and mixtures that include amphibole.

© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.

In plain English

This case-control study re-analysed a US study of people who died after a mesothelioma diagnosis between 1975 and 1980, compared with people who died of other causes. The main analysis covered 176 white men with mesothelioma and 404 white male controls. Work histories came from interviews with next of kin. A job-exposure matrix and expert review then assigned asbestos fiber types and lengths to each person. Men exposed only to chrysotile were analysed as one combined group (long fibers only, short fibers only, or both); compared with unexposed men, this group as a whole had an odds ratio of 3.8 (95% CI 1.3 to 11.2). The highest odds ratio, 12.8 (95% CI 4.1 to 40.2), was for a mixture of extra-long amosite, short and long chrysotile, tremolite and anthophyllite. Risk was increased for every asbestos type. The chrysotile-only risk was lower than that mixture's, but the difference was not statistically significant (p=0.10). The authors noted that next-of-kin reports could misclassify exposure and that some exposure groups had few cases. They concluded that asbestos regulation should target both pure chrysotile and mixtures containing amphibole.

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: Case-control study: a new analysis of next-of-kin interview data from an earlier US case-control study of mesothelioma (1975-1980), using a job-exposure matrix and expert review to assign fiber types and lengths
• Who was studied: 176 white men who had died with mesothelioma (cases) and 404 white men who had died of causes other than cancer, respiratory disease, violence or suicide (controls). They were drawn from a larger group of 201 non-Hispanic white cases diagnosed 1975-1980 and 509 controls. The cases were identified through the New York State cancer registry, the Los Angeles County cancer surveillance program and 39 Veterans Administration hospitals. Women (25 cases, 105 controls) were included only in a secondary analysis.
• Exposure: Lifetime occupational asbestos exposure, assigned from next-of-kin reports, a job-exposure matrix and expert review. Fibers were chrysotile (short: 4 micrometres or less; long: over 4 micrometres), amosite (short, medium, long and extra-long), tremolite, anthophyllite and crocidolite. Categories included chrysotile only and nine chrysotile-amphibole mixtures. They were compared with an unexposed group (20 cases, 175 controls).
• Main results:
  • Men exposed only to chrysotile were analysed as one combined category (6 cases, 14 controls) that pooled long chrysotile only, short chrysotile only, and both short and long chrysotile. Compared with unexposed men, this category as a whole had an odds ratio of 3.8 (95% CI 1.3 to 11.2). The figure applies to the pooled group, not to each fiber length separately.
  • The mixture of extra-long amosite, short and long chrysotile, tremolite and anthophyllite (9 cases, 6 controls) had the highest odds ratio: 12.8 (95% CI 4.1 to 40.2).
  • The mixture of extra-long amosite and short chrysotile (54 cases, 44 controls) had an odds ratio of 10.7 (95% CI 5.7 to 19.9).
  • Mesothelioma risk was increased for every asbestos type studied, and the size of the risk differed by fiber type.
  • The authors described suggestive evidence of overall differences in risk across the exposure categories (p heterogeneity=0.02).
  • The risk for chrysotile only was lower than for the complex mixture, but this difference was not statistically significant (p=0.10).
  • Differences in risk driven by fiber length alone were unclear.
  • Results were similar when women were included in the analysis.
• The authors' conclusion: The authors concluded that their findings suggest asbestos regulation should target both pure chrysotile and mixtures containing amphibole.
• Limitations the authors state:
  • Next-of-kin reports may have misclassified exposure, which could bias the estimates in either direction.
  • Some exposure categories had few cases, which may have reduced the ability to detect differences in risk by fiber type or length.
  • Some subjects fell into more than one exposure group.
  • Individual data on how long and how intensely each person was exposed to specific fiber types and lengths were not available.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chrysotile, Amphibole Group, Case-Control Study, Asbestos Exposure, Amosite, Tremolite, Anthophyllite.

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