Malignant pleural mesothelioma in US automotive mechanics: reported vs expected number of cases from 1975 to 2007

Our plain-English summary of Malignant pleural mesothelioma in US automotive mechanics: reported vs expected number of cases from 1975 to 2007, by B.L. Finley, J.S. Pierce, D.J. Paustenbach, et al (Regulatory Toxicology and Pharmacology, 2012).

The study

• Authors: B.L. Finley, J.S. Pierce, D.J. Paustenbach, L.L. Scott, L. Lievense, P.K. Scott, D.A. Galbraith
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2012;64(1):104-16
• Type of article: Review
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Until the 1980s, chrysotile asbestos was a component of automotive brakes manufactured in the US. The current OSHA Bulletin (2006) for brake repair cites a single study (Lemen, 2004) which concluded that the number of mesothelioma cases reported in the literature in "end-product users of friction materials" indicated an asbestos-related risk for auto mechanics. However, Lemen (2004) did not compare the reported number of cases to an "expected" value, even though pleural mesothelioma occurs in the general population in the absence of asbestos exposure. We compare the number of malignant pleural mesothelioma (MPM) cases reported in the US literature among auto mechanics between 1975-2007 to an expected value derived from estimated numbers of current and former auto mechanics. A total of 106 cases categorized as mesothelioma or malignant neoplasm of the pleura were found in the literature. Using background incidence rates for MPM of two and three cases per million individuals per year, we estimated that a range of 278-515 cases of non-asbestos-related MPM, respectively, would have occurred in current or former auto mechanics from 1975-2007. Our findings are consistent with the numerous epidemiology studies that have found no increased risk of MPM in auto mechanics.

Copyright © 2012 Elsevier Inc. All rights reserved.

In plain English

This was a literature review with a calculation of expected case numbers. The authors said it was not a formal statistical or epidemiologic study. They searched articles, books and government reports for US mechanics diagnosed with or dying of mesothelioma or malignant neoplasm of the pleura from 1975 to 2007. They found 22 documents describing 172 potential cases, 169 of them unique, and judged 106 to have been professional automotive mechanics. From labor statistics they estimated about 172 million person-years among current and former US auto mechanics. They applied background pleural mesothelioma rates of two and three cases per million per year, based on rates in US women. On that basis they estimated 344 and 516 cases would be expected without asbestos. Other assumptions gave 252 to 586. The 106 reported cases were 31% and 21% of the two main expected numbers. The authors judged that 29 of the 106 very likely or certainly had amphibole exposure in other jobs. The authors concluded the reported count could easily be due to chance. They cautioned that this is not evidence that mechanics have no increased risk, because not all cases are published.

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: Literature review of published case counts with a 'bounding analysis' comparing reported cases to an expected number calculated from labor statistics and background incidence rates; the authors state it is not a formal statistical analysis or epidemiologic study
• Who was studied: Published reports (1975 to 2007) of US mechanics diagnosed with or dying of mesothelioma or malignant neoplasm of the pleura: 22 documents, 172 potential cases, 169 unique cases, of which 106 were assumed to be professional automotive mechanics. Expected numbers were based on the estimated population of current and former US male auto mechanics.
• Exposure: Work as a US automotive mechanic. The authors note that US brake pads and clutch facings typically contained 30% to 60% chrysotile asbestos until the mid-1980s, citing an earlier review. This study did not measure exposures. It looked for amphibole (amosite and crocidolite) exposure from other jobs, such as shipbuilding and insulation work.
• Main results:
  • Of 169 unique cases found in the literature, 106 were assumed to have been professional automotive mechanics at some point in their working lives.
  • Current and former US auto mechanics were estimated to contribute about 172 million person-years over 1975 to 2007.
  • At background rates of two and three cases per million person-years, 344 and 516 non-asbestos-related mesothelioma cases were expected among auto mechanics for 1975 to 2007.
  • Under alternative assumptions the expected numbers ranged as low as 252 (life table method, two cases per million per year).
  • Under alternative assumptions the expected numbers ranged as high as 586 (age of entry 20, three cases per million per year).
  • The 106 professional automotive mechanic cases were 31% and 21% of the expected numbers at the two background rates.
  • All 169 cases among people who did some work as a 'mechanic' were 49% and 33% of the expected numbers at the two background rates.
  • The authors judged that 29 of the 106 cases very likely or certainly had amphibole exposure in another occupation, based on job histories or lung fiber burdens.
• The authors' conclusion: The authors concluded that, contrary to Lemen (2004), the number of reported cases among auto mechanics can easily be due to chance alone. They said their findings are consistent with epidemiology studies that they describe as reporting no increased risk of pleural mesothelioma in auto mechanics.
• Limitations the authors state:
  • The authors state their analysis should not be construed as evidence that auto mechanics are not at increased risk, because published cases are certain to be fewer than all cases.
  • Not all cases are reported in the literature.
  • The background incidence rates used were not adjusted for age. The authors say this would make the expected number too low.
  • Using women's rates as the background rate for men assumes that very few US women develop pleural mesothelioma from asbestos, and that non-asbestos mesothelioma rates are similar in men and women.
  • No minimum latency or job tenure was required for cases.
  • The case total likely included cases diagnosed before 1975.
  • Some cases with no stated tumor site may have been peritoneal rather than pleural mesothelioma.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Chrysotile, OSHA, Mesothelioma, Asbestos Exposure, Neoplasm, Pleura, Incidence.

Related studies

• Response to a letter to the editor by Dr. Murray M. Finkelstein regarding the article by Finley et al. (2012) — B.L. Finley, J.S. Pierce, et al. (2013)
• Asbestos exposure among transmission mechanics in automotive repair shops — N. Salazar, M.F. Cely-García, et al. (2015)
• An evaluation of short-term exposures of brake mechanics to asbestos during automotive and truck brake cleaning and machining activities — R.O. Richter, B.L. Finley, et al. (2009)
• An evaluation of reported no-effect chrysotile asbestos exposures for lung cancer and mesothelioma — J.S. Pierce, M.A. McKinley, et al. (2008)
• Increased lung cancer mortality among chrysotile asbestos textile workers is more strongly associated with exposure to long thin fibres — D. Loomis, J.M. Dement, et al. (2012)
• Letter concerning the paper by Finley and colleagues: dx.doi.org/10.1016/j.yrtph.2012.05.015 — M.M. Finkelstein (2013)

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