Epidemiological evidence indicates asbestos causes laryngeal cancer

Our plain-English summary of Epidemiological evidence indicates asbestos causes laryngeal cancer, by A.H. Smith, M.A. Handley, R. Wood (Journal of Occupational Medicine., 1990).

The study

• Authors: A.H. Smith, M.A. Handley, R. Wood
• Journal: Journal of Occupational Medicine.
• Published: 1990;32(6):499-507
• Type of article: Meta-analysis
• Cited by: 38 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000041).

Abstract

A variety of opinions have been expressed in the literature concerning asbestos and laryngeal cancer. This paper presents an analysis of epidemiological studies based on criteria that prioritized the most heavily exposed cohorts. Emphasis was given to the six cohorts or subcohorts with lung cancer relative risk estimates of 2 or more. The two groups of workers with the highest lung cancer relative risk estimates (4.06 and 3.28) both gave strong support for a causal association of asbestos and laryngeal cancer, with relative risk estimates of 1.91 (90% confidence limits 1.00 to 3.34) and 3.75 (90% confidence limits 1.01 to 9.68), respectively. Confounding with cigarette smoking or alcohol consumption does not explain the findings. Case-control studies gave mixed results, but generally supported the hypothesis. It was concluded that asbestos is a probable cause of laryngeal cancer in view of the reasonable consistency of the studies, the strength of the association in key studies, the evidence for dose-response relationships, and the biological plausibility for asbestos being a cause of laryngeal cancer.

In plain English

This was a review of published epidemiological studies on asbestos exposure and cancer of the larynx (voice box). Because good exposure measurements were rare, the authors used each cohort's lung cancer risk as a stand-in for exposure level. They prioritized six cohorts or subcohorts with lung cancer relative risks of 2 or more and did not statistically pool results. The two groups with the highest lung cancer risks were US insulators and severely exposed factory workers. Their laryngeal cancer mortality ratios were 1.91 (90% confidence limits 1.00 to 3.34) and 3.75 (1.01 to 9.68). Four of the six prioritized cohorts supported an association. Two did not, but with wide confidence limits. Case-control studies gave mixed results, but the authors judged that they generally supported the hypothesis. In an analysis of insulators at least 20 years from first exposure, adjusting for smoking raised the relative risk for larynx, pharynx and buccal cavity (mouth) cancers combined from 1.6 to 2.8. The authors judged confounding by alcohol highly unlikely. Animal studies had not shown that asbestos causes laryngeal cancer. The authors concluded that asbestos is a probable cause of laryngeal cancer.

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: Review of published epidemiological studies (cohort and case-control). The authors call it a metanalysis but did not statistically pool results; they compared relative risks and confidence limits qualitatively.
• Who was studied: Published cohort studies of asbestos-exposed workers, with emphasis on six cohorts or subcohorts that had lung cancer relative risks of 2 or more and at least 0.5 expected laryngeal cancers. Also six laryngeal cancer case-control studies and two studies of pleural plaques and laryngeal cancer.
• Exposure: Occupational asbestos exposure, with lung cancer relative risk used as a marker of how heavy the exposure was. Prioritized groups were US insulators, severely exposed factory workers, retired asbestos company workers, chrysotile miners (Italy, and Quebec), and dockyard workers in Genoa.
• Main results:
  • US insulator cohort (lung cancer SMR 4.06): 9 laryngeal cancer deaths against 4.7 expected, laryngeal cancer SMR 1.91 (90% confidence limits 1.00 to 3.34).
  • Severely exposed factory workers in the Newhouse et al study (lung cancer SMR 3.28): laryngeal cancer SMR 3.75 (90% confidence limits 1.01 to 9.68).
  • Retired asbestos company workers (lung cancer SMR 2.71): laryngeal cancer SMR 1.14 in Table 1 (90% confidence limits 0.20 to 3.59).
  • Chrysotile miners, higher versus lower exposure (lung cancer relative risk 2.54): laryngeal cancer relative risk 2.57, based on 5 cases. No confidence limits could be calculated.
  • Genoa dockyard workers: lung cancer SMR 2.24 and laryngeal cancer SMR 1.96 (90% confidence limits 1.21 to 3.01).
  • Quebec chrysotile miners, highest-exposure subcohort (lung cancer relative risk 2.25): laryngeal cancer SMR 0.81, with broad confidence limits up to 2.54.
  • Two of the six prioritized cohorts did not support the association. The authors considered this weak evidence against it because the upper confidence limits were 3.59 and 2.54.
  • Case-control studies gave mixed results, but the authors judged that they generally supported the hypothesis.
  • In the Stell and McGill case-control study, 31 of 100 laryngeal cancer cases had particular asbestos-exposed jobs, compared with 3 of 100 controls. Table 2 gives the odds ratio as 14.5.
  • In the largest case-control study (Olsen and Sabroe, Denmark), the relative risk for asbestos exposure was 1.8 and did not change after adjustment for smoking and alcohol.
  • In a Swedish study, 14 of 156 laryngeal cancer cases (9%) had bilateral pleural plaques, compared with 1.6% of men over 40 in a general health survey. The authors calculated an odds ratio of 6.1 (90% confidence limits 4.0 to 9.1).
  • US insulators, analysis limited to workers at least 20 years from first exposure: after adjustment for smoking, the relative risk for cancers of the larynx, pharynx and buccal cavity combined increased from 1.6 to 2.8.
  • The insulator smoking-adjustment figures cover only workers 20 or more years from first exposure, so they differ slightly from the Table 1 figures.
  • In a hypothetical calculation, a relative risk above 1.5 caused only by drinking would require workers to have 5 times the general population's proportion of heavy drinkers and only 5% nondrinkers. The authors rejected alcohol as a highly unlikely explanation.
• The authors' conclusion: The authors concluded that asbestos exposure is a probable cause of laryngeal cancer. They based this on reasonable consistency across studies, the suggestion of a dose-response relationship, biological plausibility, and their view that the associations are unlikely to be due to bias.
• Limitations the authors state:
  • Good quantitative data on asbestos exposure levels were rarely available, so lung cancer risk was used as a marker instead.
  • None of the prioritized cohort studies gave data on alcohol consumption.
  • There is no evidence from animal studies that asbestos causes laryngeal cancer. The authors said this does not carry much weight, because animals exposed to cigarette smoke also have not shown increased laryngeal cancer.
  • One case-control study was not assessed in detail because it was in a foreign language.

Topics

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

Medical terms in this study, explained in our Lexicon: Laryngeal Cancer, Lung Cancer, Relative Risk, Confounding, Dose-response relationship, Biological Plausibility.

Related studies

• The joint effect of asbestos exposure, tobacco smoking and alcohol drinking on laryngeal cancer risk: evidence from the French population-based case-control study, ICARE — G. Menvielle, A. Fayossé, et al. (2016)
• Asbestos, dental X-rays, tobacco, and alcohol in the epidemiology of laryngeal cancer — M.W. Hinds, D.B. Thomas, et al. (1979)
• Asbestos and laryngeal carcinoma — P.M. Stell, T. McGill (1973)
• Occupational risk factors for laryngeal carcinoma: Connecticut, 1975-1980 — R.T. Zagraniski, J.L. Kelsey, et al. (1986)
• Exposure to asbestos and laryngeal carcinoma — P.M. Stell, T. McGill (1975)
• Asbestos and lung cancer: an analysis of the epidemiological evidence on the asbestos-smoking interaction — R. Saracci (1977)

Browse more research in Journal of Occupational Medicine., or return to medical research.