Time-dependent effect of intensity of smoking and of occupational exposure to asbestos on the risk of lung cancer: results from the ICARE case-control study

Our plain-English summary of Time-dependent effect of intensity of smoking and of occupational exposure to asbestos on the risk of lung cancer: results from the ICARE case-control study, by E. Lévêque, A. Lacourt, D. Luce, et al (Occupational and Environmental Medicine, 2018).

The study

• Authors: E. Lévêque, A. Lacourt, D. Luce, M.P. Sylvestre, P. Guénel, I. Stücker, K. Leffondré
• Journal: Occupational and Environmental Medicine
• Published: 2018;75(8):586-592
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To estimate the impact of intensity of both smoking and occupational exposure to asbestos on the risk of lung cancer throughout the whole exposure history.

Methods: Data on 2026 male cases and 2610 male controls came from the French ICARE (Investigation of occupational and environmental causes of respiratory cancers) population-based, case-control study. Lifetime smoking history and occupational history were collected from standardised questionnaires and face-to-face interviews. Occupational exposure to asbestos was assessed using a job exposure matrix. The effects of annual average daily intensity of smoking (reported average number of cigarettes smoked per day) and asbestos exposure (estimated average daily air concentration of asbestos fibres at work) were estimated using a flexible weighted cumulative index of exposure in logistic regression models.

Results: Intensity of smoking in the 10 years preceding diagnosis had a much stronger association with the risk of lung cancer than more distant intensity. By contrast, intensity of asbestos exposure that occurred more than 40 years before diagnosis had a stronger association with the risk of lung cancer than more recent intensity, even if intensity in the 10 years preceding diagnosis also had a significant effect.

Conclusion: Our results illustrate the dynamic of the effect of intensity of both smoking and occupational exposure to asbestos on the risk of lung cancer. They confirm that the timing of exposure plays an important role, and suggest that standard analytical methods assuming equal weights of intensity over the whole exposure history may be questionable.

© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

In plain English

This French case–control study (ICARE, 10 départements, 2001–2007) examined how the timing of smoking and of workplace asbestos exposure related to lung cancer in men. It included 2026 men with lung cancer and 2610 men without it. Asbestos exposure was estimated from job histories using a job exposure matrix; smoking was based on reported cigarettes per day. Asbestos intensity received 40 to 60 years before diagnosis tended to have a stronger association with lung cancer than more recent intensity. For 50–60 years before diagnosis the odds ratio was 1.46 (95% CI 1.21 to 1.73) per 1 fiber/mL difference in each year, though confidence intervals were wide beyond 50 years. Asbestos intensity in the last 10 years was also significantly associated. Comparing otherwise identical histories, 1 fiber/mL/day more in each of those years gave an odds ratio of 1.20 (95% CI 1.10 to 1.31). For smoking, intensity in the last 10 years had by far the strongest association. The authors concluded that discounting recent exposures in lung cancer studies may be questionable for both smoking and asbestos. They noted that histories were self-reported and that they did not study the smoking–asbestos interaction.

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: Population-based case–control study (analysis of the ICARE study, men and lung cancer only), using logistic regression with a flexible weighted cumulative index of exposure
• Who was studied: 2026 male lung cancer cases aged 18–75 and 2610 male controls from 10 French départements, 2001–2007. These were drawn from 2276 cases and 2780 controls; 250 cases and 170 controls were excluded for missing smoking or job data.
• Exposure: Occupational asbestos exposure estimated with a job exposure matrix as annual average daily concentration of asbestos fibres in workplace air (fiber type not specified; job intensity ranged from 0.0005 to 20 equivalent fibres per mL), combined with probability and frequency of exposure. Smoking was measured as reported average cigarettes smoked per day.
• Main results:
  • A higher proportion of cases than controls had ever been occupationally exposed to asbestos: 1417 cases (69.9%) versus 1520 controls (58.2%).
  • Asbestos intensity received 40–60 years before diagnosis tended to have a stronger impact than more recent intensity. Confidence intervals were large beyond 50 years because fewer subjects contributed.
  • Odds ratio for lung cancer per 1 fiber/mL difference in asbestos intensity each year of the window: 1.33 (95% CI 1.15 to 1.52) for 40–50 years before diagnosis.
  • Odds ratio for lung cancer per 1 fiber/mL difference in asbestos intensity each year of the window: 1.46 (95% CI 1.21 to 1.73) for 50–60 years before diagnosis.
  • Asbestos intensity in the 10 years before diagnosis was significantly associated with lung cancer. Comparing subjects with otherwise identical lifetime asbestos intensity, the OR was 1.20 (95% CI 1.10 to 1.31) for a difference of 1 fiber/mL/day in each of the last 10 years.
  • Asbestos intensity received at ages 15–25 had a much stronger impact than intensity at later ages (OR 1.29, 95% CI 1.15 to 1.49, per 1 fiber/mL for ages 15–25).
  • Smoking intensity in the 10 years before diagnosis had by far the strongest contribution to lung cancer risk compared with more distant smoking (OR 2.02, 95% CI 1.96 to 2.36, per 10 cigarettes/day each year of that window).
  • The data did not suggest that smoking at ages 15–25 had a stronger impact than smoking at later ages, although smoking at those ages was significantly associated with risk (OR 1.32, 95% CI 1.22 to 1.45, per 10 cigarettes/day).
  • Results were similar when further adjusted for education.
• The authors' conclusion: The authors concluded that the timing of exposure matters. Smoking in the 10 years before diagnosis had a much stronger association with lung cancer than earlier smoking. Asbestos intensity more than 40 years before diagnosis appeared to have a stronger effect than more recent intensity, though recent asbestos intensity also had a significant effect. They concluded that discounting recent exposures in lung cancer studies may be questionable for both smoking and asbestos.
• Limitations the authors state:
  • Smoking and job histories were self-reported, and exposures far in the past may have had more measurement error.
  • The spline method can be sensitive to the number and position of knots, especially where few subjects were exposed. This gave wide confidence intervals for exposure more than 50 years before diagnosis, so results for that window should be interpreted with caution.
  • The model assumed a linear effect of intensity at each time, although smoking effects may plateau at high intensity.
  • Time before diagnosis and age at exposure are highly correlated, so their effects are hard to separate.
  • The interaction between smoking and asbestos was not investigated.

Topics

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

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Lung Cancer, Case-Control Study, Exposure History, Occupational History, Asbestos Exposure.

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