Asbestos, asbestosis, smoking, and lung cancer. New findings from the North American insulator cohort

Our plain-English summary of Asbestos, asbestosis, smoking, and lung cancer. New findings from the North American insulator cohort, by S.B. Markowitz, S.M. Levin, A. Miller, et al (American Journal of Respiratory and Critical Care Medicine, 2013).

The study

• Authors: S.B. Markowitz, S.M. Levin, A. Miller, A. Morabia
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 2013;188(1):90-6
• Cited by: 125 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Rationale: Asbestos, smoking, and asbestosis increase lung cancer risk in incompletely elucidated ways. Smoking cessation among asbestos-exposed cohorts has been little studied.

Objectives: To measure the contributions of asbestos exposure, asbestosis, smoking, and their interactions to lung cancer risk in an asbestos-exposed cohort and to describe their reduction in lung cancer risk when they stop smoking.

Methods: We examined lung cancer mortality obtained through the National Death Index for 1981 to 2008 for 2,377 male North American insulators for whom chest X-ray, spirometric, occupational, and smoking data were collected in 1981 to 1983 and for 54,243 non-asbestos-exposed blue collar male workers from Cancer Prevention Study II for whom occupational and smoking data were collected in 1982.

Measurements And Main Results: Lung cancer caused 339 (19%) insulator deaths. Lung cancer mortality was increased by asbestos exposure alone among nonsmokers (rate ratio = 3.6 [95% confidence interval (CI), 1.7-7.6]), by asbestosis among nonsmokers (rate ratio = 7.40 [95% CI, 4.0-13.7]), and by smoking without asbestos exposure (rate ratio = 10.3 [95% CI, 8.8-12.2]). The joint effect of smoking and asbestos alone was additive (rate ratio = 14.4 [95% CI, 10.7-19.4]) and with asbestosis, supra-additive (rate ratio = 36.8 [95% CI, 30.1-45.0]). Insulator lung cancer mortality halved within 10 years of smoking cessation and converged with that of never-smokers 30 years after smoking cessation.

Conclusions: Asbestos increases lung cancer mortality among nonsmokers. Asbestosis further increases the lung cancer risk and, considered jointly with smoking, has a supra-additive effect. Insulators benefit greatly by quitting smoking.

In plain English

This study compared lung cancer deaths from 1981 to 2008 among 2,377 male North American insulators, examined in 1981 to 1983, with deaths among 54,243 blue collar men from the Cancer Prevention Study II who reported no asbestos exposure. The article does not name fiber types. Lung cancer caused 339 (19.0%) insulator deaths. Compared with nonsmokers without asbestos exposure, the lung cancer rate ratio was 3.6 (95% CI 1.7 to 7.6) for nonsmoking insulators without asbestosis on chest X-ray, 10.3 (8.8 to 12.2) for smokers in the comparison group, and 14.4 (10.7 to 19.4) for smoking insulators without asbestosis, a combined effect the authors called additive. It was 7.4 (4.0 to 13.7) for nonsmoking insulators with asbestosis and 36.8 (30.1 to 45.0) for smoking insulators with asbestosis, which they called supra-additive. The insulators' rate ratio fell from 53.7 to 26.6 within 10 years of quitting smoking. At 30 or more years after quitting it was 5.8 (95% CI 2.2 to 11.4), based on six deaths, similar to never-smoking insulators. The authors noted that smoking and asbestosis were assessed only once.

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: Cohort mortality study comparing an asbestos-exposed insulator cohort with an unexposed blue collar comparison group (Poisson regression for between-group comparisons, Cox models within insulators)
• Who was studied: 2,377 male North American insulators aged 40 or older with 20 or more years as insulators, examined 1981 to 1983 (about 40% of those invited took part), followed to 2008; comparison group of 54,243 blue collar men from Cancer Prevention Study II with no reported asbestos exposure, followed from 1982 to 2008
• Exposure: Long-term insulation work (20 or more years) with asbestos-containing products such as cement, pipe covering or insulation spray, 1950s to 1970s; fiber types not named. Also cigarette smoking, and asbestosis (parenchymal opacities) on chest X-ray
• Main results:
  • Among insulators, lung cancer caused 339 deaths (19.0%); cancers overall caused 45.7% of deaths
  • Never-smoking insulators overall: lung cancer mortality rate ratio 5.2 (95% CI 3.2 to 8.5), based on 18 deaths among 468 men, compared with nonsmokers in the comparison group
  • Nonsmoking insulators without asbestosis on X-ray: rate ratio 3.6 (95% CI 1.7 to 7.6)
  • Smokers in the comparison group (no asbestos exposure): rate ratio 10.3 (95% CI 8.8 to 12.2)
  • Smoking insulators without asbestosis: rate ratio 14.4 (95% CI 10.7 to 19.4), described by the authors as an additive joint effect
  • Insulators with asbestosis: rate ratio 7.4 (95% CI 4.0 to 13.7) among nonsmokers and 36.8 (95% CI 30.1 to 45.0) among smokers, described as supra-additive
  • All smoking insulators: rate ratio 28.4, a joint effect the authors found more than additive
  • The authors found the overall combined effect of asbestos and smoking was supra-additive, not multiplicative
  • Among insulators, the lung cancer mortality rate ratio fell from 53.7 to 26.6 during the first 10 years after quitting smoking
  • Insulators 30 or more years after quitting: rate ratio 5.8 (95% CI 2.2 to 11.4), based on six lung cancer deaths, similar to the rate ratio of 5.3 among never-smoking insulators
  • After quitting smoking, rate ratios of insulators without asbestosis declined in parallel with comparison-group former smokers (additive pattern)
• The authors' conclusion: The authors concluded that asbestos exposure without asbestosis raises lung cancer risk among nonsmokers and adds to the risk of smoking, and that asbestosis further increases risk, with a supra-additive effect when combined with smoking
• Limitations the authors state:
  • Smoking status and asbestosis were assessed only once and may have changed later, causing misclassification
  • Asbestosis can exist without findings on chest X-ray, so some cases may have been misclassified
  • Some comparison-group members may have had short-term asbestos exposure; the authors state this would lead to underestimating the risk from asbestos
  • The narrow range of heavy long-term exposure limits how far the findings apply to lower asbestos exposures

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Insulator, Asbestos Exposure, Chest X-Ray, rate ratio, confidence interval.

Related studies

• Radiographic abnormalities in asbestos insulators: effects of duration from onset of exposure and smoking. Relationships of dyspnea with parenchymal and pleural fibrosis — R. Lilis, A. Miller, et al. (1991)
• Spirometric impairments in long-term insulators. Relationships to duration of exposure, smoking, and radiographic abnormalities — A. Miller, R. Lilis, et al. (1994)
• Asbestosis: interstitial pulmonary fibrosis and pleural fibrosis in a cohort of asbestos insulation workers: influence of cigarette smoking — R. Lilis, I.J. Selikoff, et al. (1986)
• Airways obstruction from asbestos exposure. Effects of asbestosis and smoking — K.H. Kilburn, R.H. Warshaw (1994)
• Effects of asbestos and smoking on gas diffusion in people exposed to crocidolite — H.S. Alfonso, L. Fritschi, et al. (2005)
• Non-Malignant Respiratory Illnesses in Association with Occupational Exposure to Asbestos and Other Insulating Materials: Findings from the Alberta Insulator Cohort — S. Moitra, A. Farshchi Tabrizi, et al. (2020)

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