Mesothelioma among Motor Vehicle Mechanics: An Updated Review and Meta-analysis

Our plain-English summary of Mesothelioma among Motor Vehicle Mechanics: An Updated Review and Meta-analysis, by D.H. Garabrant, D.D. Alexander, P.E. Miller, et al (The Annals of Occupational Hygiene, 2016).

The study

• Authors: D.H. Garabrant, D.D. Alexander, P.E. Miller, J.P. Fryzek, P. Boffetta, M.J. Teta, P.A. Hessel, V.A. Craven, M.A. Kelsh, M. Goodman
• Journal: The Annals of Occupational Hygiene
• Published: 2016;60(1):8-26
• Type of article: Meta-analysis, Systematic review
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: We published a meta-analysis of the association between work as a motor vehicle mechanic and mesothelioma in 2004. Since then, several relevant studies on this topic have been published. Thus, to update the state-of-the-science on this issue, we conducted a new systematic review and meta-analysis.

Methods: A comprehensive PubMed literature search through May 2014 was conducted to identify studies that reported relative risk estimates for mesothelioma among motor vehicle mechanics (in general), and those who were engaged in brake repair (specifically). Studies were scored and classified based on study characteristics. Random-effects meta-analyses generated summary relative risk estimates (SRREs) and corresponding 95% confidence intervals (CI). Heterogeneity of results was examined by calculating Q-test P-values (P-H) and I (2) estimates. Sub-group and sensitivity analyses were conducted for relevant study characteristics and quality measures.

Results: Ten case-control studies, one cohort study, and five proportionate mortality ratio (PMR)/standardized mortality odds ratio (SMOR) studies were identified and included in the quantitative assessment. Most meta-analysis models produced SRREs below 1.0, and no statistically significant increases in mesothelioma were observed. The SRRE for all studies was 0.80 (95% CI: 0.61-1.05) with significant heterogeneity (P-H <0.001, I (2) = 62.90). A similar SRRE was observed among the five Tier 1 studies with the highest quality ratings (SRRE = 0.76, 95% CI: 0.46-1.25), with no heterogeneity among studies (P-H = 0.912, I (2) = 0.00). Meta-analysis of the Tier 2 (n = 5) and Tier 3 (n = 6) studies resulted in SRREs of 1.09 (95% CI: 0.76-1.58) and 0.73 (95% CI: 0.49-1.08), respectively. Restricting the analysis to Tiers 1 and 2 combined resulted in an SRRE of 0.92 (95% CI: 0.72-1.29). The SRRE specific to brake work (n = 4) was 0.64 (95% CI: 0.38-1.09).

Conclusions: This meta-analysis of the epidemiologic studies provides evidence that motor vehicle mechanics, including workers who were engaged in brake repair, are not at an increased risk of mesothelioma.

© The Author 2015. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

In plain English

This was a systematic review and meta-analysis. It pooled the results of earlier studies rather than collecting new data. The authors searched PubMed and Embase through May 2014. They pooled 16 studies of motor vehicle mechanics published from 1980 to 2013, mostly case-control studies, and grouped them into three quality tiers. Across all 16 studies the summary relative risk of mesothelioma was 0.80 (95% CI 0.61–1.05). For the five highest-quality studies it was 0.76 (0.46–1.25). For four studies with brake-work data it was 0.66 (0.39–1.10); the summary table prints 0.64 (0.38–1.09). None of these was statistically significant. One Massachusetts registry study reported a significantly raised estimate of 2.1 (1.1–4.0). The authors treated it as an outlier with the lowest quality score. A test for publication bias gave a P-value of 0.05. The authors concluded that neither motor vehicle mechanic work nor brake repair work is associated with an increased risk of mesothelioma. They acknowledged that classifying exposure by job title could in theory miss an association.

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: Updated systematic review and meta-analysis of published epidemiologic studies, using random-effects models and quality scoring of studies into three tiers
• Who was studied: 16 studies (ten case-control, one cohort, five proportionate mortality ratio or standardized mortality odds ratio studies) published 1980 to 2013, found by searching PubMed and Embase through May 2014. The studies were from the USA, Canada, Europe and Mexico.
• Exposure: Work as a motor vehicle mechanic in general, and brake repair work specifically. The background describes possible exposure to short chrysotile fibers from brakes, clutches and gaskets. In most included studies, exposure was defined by job title.
• Main results:
  • All 16 studies combined: summary relative risk 0.80 (95% CI 0.61–1.05), with statistically significant heterogeneity between studies
  • Five Tier 1 (highest quality) studies: summary relative risk 0.76 (95% CI 0.46–1.25), with no heterogeneity
  • Five Tier 2 studies: summary relative risk 1.09 (95% CI 0.76–1.58), not statistically significant
  • Six Tier 3 studies: summary relative risk 0.73 (95% CI 0.49–1.08). With the Roelofs study removed, the Tier 3 estimate was 0.59, which was statistically significant (95% CI 0.44–0.79).
  • Tier 1 and Tier 2 studies combined (10 studies): summary relative risk 0.96 (95% CI 0.72–1.29), not statistically significant
  • Four studies with data specific to brake work: summary relative risk 0.66 (95% CI 0.39–1.10) in the text. Table 3 prints 0.64 (0.38–1.09).
  • One included study (Roelofs et al., 2013, Massachusetts Cancer Registry) found 10 automobile mechanics among 564 occupation-coded mesothelioma cases, with a standardized morbidity odds ratio of 2.1 (95% CI 1.1–4.0). The authors identified it as an outlier.
  • Egger's test for publication bias gave a P-value of 0.05. A trim-and-fill adjustment changed the overall estimate from 0.80 (95% CI 0.61–1.05) to 0.52 (95% CI 0.39–0.69).
• The authors' conclusion: The authors concluded that neither work as a motor vehicle mechanic nor work in brake repair is associated with an increased risk of mesothelioma.
• Limitations the authors state:
  • Classifying exposure by job title could in theory miss an association if exposure was low level or infrequent
  • Some individual studies had limited statistical power
  • Statistical testing for publication bias gave significant results
  • Many quality-scoring criteria reflected inherent features of the study designs and underlying data

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, Meta-Analysis, Systematic Review, Relative Risk, confidence interval, P-Value, Cohort Study, Odds Ratio.

Related studies

• Response to Kay Teschke. Re: Mesothelioma among Motor Vehicle Mechanics: An Updated Review and Meta-analysis — D.H. Garabrant, D.D. Alexander, et al. (2016)
• Mesothelioma and lung cancer among motor vehicle mechanics: a meta-analysis — M. Goodman, M.J. Teta, et al. (2004)
• Asbestos exposures of mechanics performing clutch service on motor vehicles — H.J. Cohen, D.R. Van Orden (2008)
• Malignant Mesothelioma in a Motor Vehicle Mechanic — C. Meisenkothen (2017)
• Personal exposure to asbestos and respiratory health of heavy vehicle brake mechanics — M.F. Cely-García, C.A. Torres-Duque, et al. (2015)
• Mesothelioma in vehicle mechanics: is the risk different for Australians? — M.A. Kelsh, V.A. Craven, et al. (2007)

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