Mesothelioma and lung cancer among motor vehicle mechanics: a meta-analysis

Our plain-English summary of Mesothelioma and lung cancer among motor vehicle mechanics: a meta-analysis, by M. Goodman, M.J. Teta, P.A. Hessel, et al (The Annals of Occupational Hygiene, 2004).

The study

• Authors: M. Goodman, M.J. Teta, P.A. Hessel, D.H. Garabrant, V.A. Craven, C.G. Scrafford, M.A. Kelsh
• Journal: The Annals of Occupational Hygiene
• Published: 2004;48(4):309-26
• Type of article: Meta-analysis, Systematic review
• Cited by: 71 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We conducted a systematic review and analysis of the epidemiological literature that examines the risk of lung cancer and mesothelioma among motor vehicle mechanics who may have been engaged in brake repair and, thus, were potentially exposed to asbestos. All relevant studies were classified into three tiers according to their quality. Tier III (lowest quality) studies were cited for completeness, but were not included in the meta-analysis. Meta relative risks (meta-RRs) were calculated for mesothelioma and lung cancer using both fixed and random effects models for Tiers I and II, separately, followed by stratified analyses based on study design or exposure characterization (garage workers versus brake workers) and, for lung cancer studies, based on adequate adjustment for smoking. The meta-analysis for Tier I (higher quality) and Tier II (lower quality) studies of mesothelioma yielded RR estimates of 0.92 (95% CI 0.55-1.56) and 0.81 (95% CI 0.52-1.28), respectively. Further stratification according to exposure characterization did not affect the results. The meta-analysis for lung cancer produced RR estimates of 1.07 (95% CI 0.88-1.31) for Tier I and 1.17 (95% CI 1.01-1.36) for Tier II. When the lung cancer analysis was limited to studies that used adequate control for smoking, the resulting RR estimate was 1.09 (95% CI 0.92-1.28). Based on these findings, we conclude that employment as a motor vehicle mechanic does not increase the risk of developing mesothelioma. Although some studies showed a small increase in risk of lung cancer among motor vehicle mechanics, the data on balance do not support a conclusion that lung cancer risk in this occupational group is related to asbestos exposure.

In plain English

This article was a systematic review and meta-analysis (pooling earlier studies) of mesothelioma and lung cancer among motor vehicle mechanics, who may have been exposed to asbestos through brake repair. The authors scored each study for quality and sorted them into tiers. The lowest-scoring Tier III studies were not pooled. For mesothelioma, seven studies were pooled. The combined relative risk was 0.92 (95% CI 0.55–1.56) for the four higher-quality Tier I studies and 0.81 (95% CI 0.52–1.28) for the three Tier II studies. For studies defining exposure as brake work it was 0.86 (95% CI 0.48–1.56). For lung cancer, nine studies were pooled: 1.07 (95% CI 0.88–1.31) for Tier I, 1.17 (95% CI 1.01–1.36) for Tier II, and 1.09 (95% CI 0.92–1.28) for the six studies that adequately adjusted for smoking. The authors concluded that motor vehicle mechanic work does not increase mesothelioma risk. They also concluded that the data on balance do not support linking these mechanics' lung cancer to asbestos. They noted that other quality-scoring approaches may exist.

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: Systematic review and meta-analysis of published and unpublished epidemiological studies. Studies were quality-scored into three tiers. Tier III (negative score) studies were excluded from pooling. Fixed and random effects models were used.
• Who was studied: Studies of motor vehicle mechanics (general mechanics excluded). Mesothelioma: 11 studies were scored and 7 were pooled (4 Tier I, 3 Tier II, all case–control), from the USA, Canada, Germany, Denmark and Spain, published 1980 to 2004. Lung cancer: 22 studies were scored and 9 were pooled (4 Tier I, 5 Tier II), published 1977 to 1992.
• Exposure: Employment in motor vehicle repair, with potential asbestos exposure from brake repair. Studies were also grouped by whether exposure was defined generally (e.g. garage workers, car mechanics) or specifically as brake work.
• Main results:
  • Mesothelioma: the pooled relative risk was 0.92 (95% CI 0.55–1.56) for Tier I studies and 0.81 (95% CI 0.52–1.28) for Tier II studies.
  • Mesothelioma: in studies that defined exposure as brake repair (3 studies), the pooled relative risk was 0.86 (95% CI 0.48–1.56).
  • Mesothelioma: in studies that took other asbestos exposures into account (4 studies), the pooled relative risk was 0.80 (95% CI 0.46–1.40).
  • Lung cancer: the pooled relative risk was 1.07 (95% CI 0.88–1.31) for Tier I studies and 1.17 (95% CI 1.01–1.36) for Tier II studies.
  • Lung cancer: in the six studies with adequate adjustment for smoking, regardless of tier, the pooled relative risk was 1.09 (95% CI 0.92–1.28).
  • Lung cancer: case–control studies gave a pooled relative risk of 1.08 (95% CI 0.87–1.34). Cohort studies gave 1.16 (95% CI 1.00–1.34).
  • When studies from all three tiers were combined, the pooled relative risk for mesothelioma was 0.67 (95% CI 0.53 to 0.84). The authors suggested this departure from 1.0 could be explained by methodological problems of individual studies.
  • When studies from all three tiers were combined, the pooled relative risk for lung cancer was 1.16 (95% CI 1.13–1.19). The authors suggested this departure from 1.0 could be explained by methodological problems of individual studies.
  • Tests for heterogeneity among the lung cancer studies were not statistically significant in any stratification.
• The authors' conclusion: The authors concluded that employment as a motor vehicle mechanic does not increase the risk of mesothelioma. They noted that some studies showed a small increase in lung cancer risk among motor vehicle mechanics, but concluded that the data on balance do not support a conclusion that this lung cancer is related to asbestos exposure from vehicle repair.
• Limitations the authors state:
  • The quality-scoring method reflected the authors' consensus, and other approaches may exist.
  • Interpreting the heterogeneity test was problematic because the studies varied widely in design, population and reference groups.
  • Three cohort studies reporting mesothelioma cases could not be included because relative risks could not be calculated.
  • Pooled estimates may not accurately reflect the size of an association unless sources of systematic error are taken into account.
  • None of the lung cancer studies included in the meta-analysis was published in the last 10 years.

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, Lung Cancer, Meta-Analysis, Systematic Review, Relative Risk, Asbestos Exposure.

Related studies

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

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