Asbestos exposure and laryngeal cancer mortality

Our plain-English summary of Asbestos exposure and laryngeal cancer mortality, by W.J. Peng, J. Mi, Y.H. Jiang (The Laryngoscope, 2016).

The study

• Authors: W.J. Peng, J. Mi, Y.H. Jiang
• Journal: The Laryngoscope
• Published: 2016;126(5):1169-74
• Type of article: Meta-analysis, Systematic review
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives/hypothesis: Occupational exposure to asbestos occurs in many workplaces and is well known to cause asbestosis, lung cancer, and mesothelioma. However, the link between asbestos exposure and other malignancies was not confirmed. The aim of the current meta-analysis was to provide a summary measure of risk for laryngeal cancer associated with occupational asbestos exposure.

Study Design: Systematic review and meta-analysis.

Methods: Electronic databases were searched for studies characterizing the association between asbestos and laryngeal cancer. Standardized mortality rate (SMR) with its 95% confidence interval (CI) of each study was combined using a fixed or random effect model.

Results: Significantly increased SMR for laryngeal cancer was observed when subjects were exposed to asbestos (SMR = 1.69, 95% CI = 1.45-1.97, P < .001), with little evidence of heterogeneity among studies (Q = 15.39, P = .803, I(2) = 0.0%). Effect estimates were larger for cohorts controlling for male subjects, Europe and Oceania, mining and textile industries, exposure to crocidolite, long study follow-up (>25 years), and SMR for lung cancer > 2.0. Publication bias was not detect by Begg test (P = .910) and Egger test (P = .340).

Conclusions: Our study supports the association of exposure to asbestos with an increased risk of laryngeal cancer mortality among male workers.

Level Of Evidence: NA Laryngoscope, 126:1169-1174, 2016.

© 2015 The American Laryngological, Rhinological and Otological Society, Inc.

In plain English

This article was a systematic review and meta-analysis of earlier published studies. The authors searched PubMed, Springer and the Cochrane library for English or Chinese studies. They combined 21 cohort studies published 1988 to 2013, covering 185 laryngeal cancer deaths or cases. The pooled standardized mortality rate (SMR) for laryngeal cancer was 1.69 (95% CI 1.45 to 1.97), with no heterogeneity between studies. The increase was statistically significant in male cohorts (1.71, 95% CI 1.33 to 2.19) but not in female cohorts (1.44, 95% CI 0.90 to 2.29). It was significant for chrysotile, crocidolite and mixed asbestos, and for mining and textile cohorts, but not for cement cohorts. Cohorts with a lung cancer SMR above 2.0, a stand-in for heavier exposure, had a pooled SMR of 2.07 (95% CI 1.54 to 2.76), versus 1.52 (95% CI 1.25 to 1.97) in cohorts with a lung cancer SMR of 2.0 or less. The authors concluded that asbestos exposure was associated with increased laryngeal cancer risk, especially in male workers. The authors noted estimates could not be adjusted for smoking or alcohol.

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 cohort studies
• Who was studied: 21 published studies of asbestos-exposed workers, found by searching for English or Chinese articles from December 31, 1980 to December 31, 2014. The studies were published 1988 to 2013, with cohort sizes from 276 to 98,117. Twelve were from Europe, four from the United States, three from Oceania and two from Asia. Together they included 185 laryngeal cancer deaths or cases.
• Exposure: Occupational asbestos exposure, either crocidolite, chrysotile or mixed asbestos. The industries included mining and milling, textiles, cement, gas mask assembly, stripping/removal work, railway carriage construction, and refinery and petrochemical plants. Individual exposure levels were not available. Instead, the authors used each cohort's lung cancer SMR (above 2.0 versus 2.0 or less) as a substitute for exposure level. One study (Reid 2004) had no lung cancer SMR reported.
• Main results:
  • All 21 studies combined: SMR for laryngeal cancer 1.69 (95% CI 1.45 to 1.97, P less than .001), with no heterogeneity (Q 15.39, I2 0.0%, P .803).
  • Male cohorts (11 studies): SMR 1.71 (95% CI 1.33 to 2.19, P less than .001). Female cohorts (4 studies): SMR 1.44 (95% CI 0.90 to 2.29, P .125), not statistically significant.
  • By industry: the results were significant for mining (4 studies), with an SMR of 2.01 (95% CI 1.46 to 2.76), and for textile (6 studies), with an SMR of 1.90 (95% CI 1.26 to 2.88). Cement (4 studies) had an SMR of 1.39 (95% CI 0.97 to 1.99, P .071), which was not significant.
  • By asbestos type, all three groups were significant: chrysotile (8 studies) SMR 1.73 (95% CI 1.17 to 2.55), crocidolite (3 studies) 1.99 (95% CI 1.41 to 2.81), and mixed asbestos (11 studies) 1.60 (95% CI 1.33 to 1.93).
  • By region: the results were significant for Europe (12 studies), with an SMR of 1.64 (95% CI 1.36 to 1.97), and for Oceania (3 studies), with an SMR of 1.99 (95% CI 1.41 to 2.81). They were not significant for Asia (2 studies), with an SMR of 2.76 (95% CI 0.94 to 8.13, P .065), or for America (4 studies), with an SMR of 1.38 (95% CI 0.85 to 2.25, P .199).
  • Studies with more than 25 years of follow-up (15 studies) had an SMR of 1.70 (95% CI 1.43 to 2.02, P less than .001). The shorter follow-up group (6 studies) had an SMR of 1.48 (95% CI 0.91 to 2.42, P .113), which was not significant.
  • Cohorts with a lung cancer SMR above 2.0 (9 studies, treated as high-exposure) had a pooled laryngeal cancer SMR of 2.07 (95% CI 1.54 to 2.76). Cohorts with a lung cancer SMR of 2.0 or less (11 studies, treated as lower-exposure) had a pooled SMR of 1.52 (95% CI 1.25 to 1.97). The authors wrote that this seems to suggest a dose-response relation.
  • The authors left out each study in turn. The pooled SMRs did not change significantly, but the authors did not show these data.
  • The Begg and Egger tests gave P values of .910 and .340. The authors took this to suggest no publication bias.
• The authors' conclusion: The authors concluded that their meta-analysis supported the hypothesis that asbestos exposure was associated with an increased risk of laryngeal cancer, especially in male workers. They called for further study of the mechanisms.
• Limitations the authors state:
  • The pooled SMRs were based on unadjusted estimates. The original cohort studies lacked data on smoking and alcohol, so these could not be adjusted for.
  • Detailed exposure assessment was often missing from the included studies, and risk by duration or level of exposure was not quantified. For this reason, the authors used lung cancer mortality as a substitute for exposure measurements.
  • The authors suggested that there may have been too few female laryngeal cancer cases to detect an association in women.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Throat and laryngeal cancer.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Laryngeal Cancer, Occupational Exposure, Lung Cancer, Mesothelioma, Meta-Analysis, Systematic Review, confidence interval.

Related studies

• Exposure to nitrosamines, carbon black, asbestos, and talc and mortality from stomach, lung, and laryngeal cancer in a cohort of rubber workers — K. Straif, U. Keil, et al. (2000)
• In reference to Asbestos exposure and laryngeal cancer mortality — M.M. Finkelstein (2017)
• The epidemiology of laryngeal cancer in Brazil — V. Wünsch Filho (2004)
• Diet and other risk factors for laryngeal cancer in Shanghai, China — W. Zheng, W.J. Blot, et al. (1992)
• Exposure to cement dust, related occupational groups and laryngeal cancer risk: results of a population based case-control study — A. Dietz, H. Ramroth, et al. (2004)
• A case-control study of occupational risk factors for laryngeal cancer — P. Wortley, T.L. Vaughan, et al. (1992)

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