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Mesothelioma risk among those exposed to chrysotile asbestos only and mixtures that include amphibole: a case–control study in the USA, 1975–1980
  1. Jason Y Y Wong1,
  2. Carol Rice2,
  3. Aaron Blair1,
  4. Debra T Silverman1
  1. 1 Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, MD, USA
  2. 2 Department of Environmental and Public Health Sciences, University of Cincinnati, Cincinnati, OH, USA
  1. Correspondence to Dr Jason Y Y Wong, Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, MD, 20850, USA; jason.wong{at}


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.

  • asbestos
  • mesothelioma
  • epidemiology
  • hygiene / occupational hygiene

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  • Contributors JW: conceptualisation/design, data analyses and manuscript preparation. CR: conceptualisation/design, exposure assessment, data analyses and manuscript preparation. AB and DTS: conceptualisation/design and manuscript preparation.

  • Funding This work was supported by intramural funding from the National Cancer Institute.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement No data are available.