Are pleural plaques an appropriate endpoint for risk analyses?

Our plain-English summary of Are pleural plaques an appropriate endpoint for risk analyses?, by L.D. Maxim, R. Niebo, M.J. Utell (Inhalation Toxicology, 2015).

The study

• Authors: L.D. Maxim, R. Niebo, M.J. Utell
• Journal: Inhalation Toxicology
• Published: 2015;27(7):321-34
• Type of article: Review
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This review summarizes the literature on the relation between the development of pleural plaques and non-malignant and malignant disease in cohorts exposed to asbestos and other fibers. The available evidence indicates that, absent any other pleural disease, the presence of pleural plaques does not result in respiratory symptoms or clinically significant impacts on lung function. For certain types of asbestos, the development of pleural plaques is statistically correlated with malignant disease, but the evidence is consistent with the hypothesis that pleural plaques without other pleural disease are a marker of exposure, rather than an independent risk factor. Pleural plaques have also developed in cohorts exposed to other fibers that have not proven to be carcinogenic. Risk analyses should be based on the avoidance of known adverse conditions, rather than pleural plaques per se.

In plain English

This article was a literature review. The authors asked whether pleural plaques, a common non-cancerous effect of asbestos, should be a risk-analysis endpoint, as the US EPA had made them for Libby Amphibole Asbestos. They reported that plaques without other pleural disease were not associated with respiratory symptoms or, in most people, clinically significant loss of lung function. They also reported broad agreement that plaques do not become cancerous. Plaques were correlated with lung cancer and mesothelioma in asbestos-exposed groups. However, the authors judged that studies adjusting for exposure mostly fit plaques being a marker of exposure, not an independent risk factor. The exceptions were two studies by Pairon and colleagues. One reported a hazard ratio of 6.8 (confidence interval 2.2 to 21.4) for pleural mesothelioma, from 17 cases. The other reported 2.41 (confidence interval 1.21 to 4.85) for lung cancer death, from 36 deaths, adjusted for smoking and cumulative asbestos exposure. The authors called these suggestive but not definitive. Plaques have also been reported after wollastonite, mineral wool and refractory ceramic fiber exposure. The authors concluded that using plaques as an adverse endpoint was not justified.

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
• Who was studied: Published studies, reviews and expert-body statements on pleural plaques in cohorts exposed to asbestos and other fibers, located through search engines and databases such as PubMed and Google Scholar. The review focused chiefly on malignant effects.
• Exposure: Asbestos of various types, and other fibers. The review was prompted partly by the US EPA choosing pleural plaques as an adverse endpoint in its risk analysis for Libby Amphibole Asbestos.
• Main results:
  • In the authors' summary, pleural plaques without other non-malignant pleural disease were not associated with respiratory symptoms or, in most individuals, with clinically significant impairment of lung function.
  • The authors described broad agreement that any effects on lung function, even if statistically significant, are small.
  • The authors described broad agreement that pleural plaques are not premalignant, meaning they do not become cancerous over time.
  • In cohorts occupationally exposed to asbestos, the presence of pleural plaques was correlated with lung cancer and mesothelioma.
  • Among the studies that tried to correct for confounders (Table 1), all except the Pairon et al. studies were, in the authors' view, consistent with plaques being a marker of exposure rather than an independent risk factor.
  • As cited by the review: Pairon et al. (2013a) found 17 incident cases of pleural mesothelioma among retired or unemployed asbestos-exposed workers. The hazard ratio for pleural plaques was 6.8 (confidence interval 2.2 to 21.4).
  • As cited by the review: Pairon et al. (2014) recorded 36 lung cancer deaths among 5402 male screening-program participants. The hazard ratio for pleural plaques was 2.41 (confidence interval 1.21 to 4.85), adjusted for smoking and a cumulative asbestos exposure index.
  • The authors called the Pairon et al. studies suggestive, saying they should not be dismissed out of hand.
  • Pleural plaques have been reported in cohorts exposed to wollastonite, mineral wool and refractory ceramic fibers. The authors found no consistent relationship between plaques and lung cancer or mesothelioma in those cohorts.
  • Apart from the 2004 American Thoracic Society review, the advisory bodies reviewed were, in the authors' view, broadly consistent with plaques being a marker of asbestos exposure.
• The authors' conclusion: The authors concluded that the available evidence does not justify choosing pleural plaques as an adverse condition for risk analysis. They concluded that exposure limits should instead be based on data linking exposure to clinically adverse health effects.
• Limitations the authors state:
  • The authors noted that, in the studies reviewed, adjusting for asbestos exposure is difficult. Plaques may go undetected depending on the imaging method, and exposure data may be missing or inaccurate.
  • The authors said further research on whether plaques are an independent risk factor is appropriate, and that the Pairon et al. results cannot be regarded as definitive.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Pleural Plaques, Carcinogenic.

Related studies

• Asbestos-related pleural diseases: dimensional criteria are not appropriate to differentiate diffuse pleural thickening from pleural plaques — J. Ameille, M. Matrat, et al. (2004)
• Modelling prevalence and incidence of fibrosis and pleural plaques in asbestos-exposed populations for screening and follow-up: a cross-sectional study — C. Paris, A. Martin, et al. (2008)
• Non-neoplastic and neoplastic pleural endpoints following fiber exposure — V.C. Broaddus, J.I. Everitt, et al. (2011)
• Asbestos exposure, pleural plaques, and the risk of death from lung cancer — J.C. Pairon, P. Andujar, et al. (2014)
• Pleural plaques as risk indicators for malignant pleural mesothelioma: a necropsy-based study — C. Bianchi, A. Brollo, et al. (1997)
• High risk of pleural plaques and parenchymal abnormalities in women living in Biancavilla (Italy) — C. Ledda, C. Loreto, et al. (2016)

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