Quantifying the mediating effects of smoking and occupational exposures in the relation between education and lung cancer: the ICARE study

Our plain-English summary of Quantifying the mediating effects of smoking and occupational exposures in the relation between education and lung cancer: the ICARE study, by G. Menvielle, J.E. Franck, L. Radoï, et al (European Journal of Epidemiology, 2016).

The study

• Authors: G. Menvielle, J.E. Franck, L. Radoï, M. Sanchez, J. Févotte, A.V. Guizard, I. Stücker, D. Luce, ICARE study group
• Journal: European Journal of Epidemiology
• Published: 2016;31(12):1213-1221
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Smoking only partly explains the higher lung cancer incidence observed among socially deprived people. Occupational exposures may account for part of these inequalities, but this issue has been little investigated. We investigated the extent to which smoking and occupational exposures to asbestos, silica and diesel motor exhaust mediated the association between education and lung cancer incidence in men. We analyzed data from a large French population-based case-control study (1976 lung cancers, 2648 controls). Detailed information on lifelong tobacco consumption and occupational exposures to various carcinogens was collected. We conducted inverse probability-weighted marginal structural models. A strong association was observed between education and lung cancer. The indirect effect through smoking varied by educational level, with the strongest indirect effect observed for those with the lowest education (OR = 1.34 (1.14-1.57)). The indirect effect through occupational exposures was substantial among men with primary (OR = 1.22 (1.15-1.30) for asbestos and silica) or vocational secondary education (OR = 1.18 (1.12-1.25)). The contribution of smoking to educational differences in lung cancer incidence ranged from 22 % (10-34) for men with primary education to 31 % (-3 to 84) for men with a high school degree. The contribution of occupational exposures to asbestos and silica ranged from 15 % (10-20) for men with a high school degree to 20 % (13-28) for men with vocational secondary education. Our results highlight the urgent need for public health policies that aim at decreasing exposure to carcinogens at work, in addition to tobacco control policies, if we want to reduce socioeconomic inequalities in the cancer field.

In plain English

This analysis of the French population-based ICARE case-control study (2001–2007) included 1976 male lung cancer cases and 2648 male controls. The authors used mediation analysis to estimate how much of the higher lung cancer risk among less-educated men ran through smoking, combined workplace exposure to asbestos and crystalline silica (estimated with job-exposure matrices), and self-reported diesel motor exhaust. Compared with university-educated men, the odds ratio for lung cancer was 3.85 (3.18–4.66) for men with primary education and 1.62 (1.28–2.04) for high school graduates. In the model with all three routes, the part running through asbestos and silica among primary-educated men, compared with university-educated men, was an odds ratio of 1.22 (1.15–1.30). That was 15% (10–20) of the total effect of education, measured on the log-odds scale. The same share was 20% (13–28) among men with vocational secondary education. Smoking accounted for 22% (10–34) among primary-educated men. Diesel exhaust contributed little. The authors concluded that smoking does not account for all educational inequalities in lung cancer. They noted possible residual confounding by smoking and missing data on other carcinogens, such as chromium VI and nickel.

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 (ICARE), analysed with mediation methods (inverse probability-weighted marginal structural models)
• Who was studied: This analysis was restricted to men from the ICARE study, conducted in 10 French départements covered by a cancer register, 2001–2007: 1976 male lung cancer cases (newly diagnosed, aged 75 or less) and 2648 male population controls who answered the full questionnaire and had complete data
• Exposure: Lifetime occupational exposure to asbestos (fiber type not specified) and crystalline silica, assessed with French job-exposure matrices and combined into one variable (never, low, high). The asbestos cut-off was 0.27 fibers/mL-years. The other exposures were diesel motor exhaust (ever/never, self-reported) and smoking (cumulative smoking index); educational level was the starting factor.
• Main results:
  • Total effect of education: compared with tertiary-educated men, the odds ratio for lung cancer was 3.85 (3.18–4.66) for men with no diploma or primary education, 2.32 (1.95–2.75) for vocational secondary and 1.62 (1.28–2.04) for high school
  • Compared with men never exposed to asbestos or silica, the odds ratio for lung cancer was 1.60 (1.39–1.84) for low combined exposure and 2.88 (2.44–3.41) for high combined exposure
  • In the model with all mediators, each group compared with tertiary-educated men, the indirect effect through asbestos and silica was: OR 1.22 (1.15–1.30), or 15% (10–20) of the total effect of education on the log-odds scale, for primary-educated men; OR 1.18 (1.12–1.25), or 20% (13–28), for vocational secondary; and OR 1.06 (1.02–1.10), or 12% (4–27), for high school
  • In the model with all mediators, the indirect effect through smoking for primary-educated men was OR 1.34 (1.14–1.57), or 22% (10–34) of the total effect on the log-odds scale. The figures were 28% (13–46) for vocational secondary and 31% (-3 to 84) for high school.
  • The indirect effect through diesel motor exhaust was small: OR 1.03 (1.00–1.07) among men with primary education
  • After accounting for all mediators, the direct effect of education stayed substantial for men with up to vocational secondary education. For men with a high school degree it was not statistically significant, although still elevated.
• The authors' conclusion: The authors concluded that smoking does not account for all social inequalities in lung cancer risk and that occupational exposures play an important part. In their view, tackling only smoking would leave large inequalities among French men.
• Limitations the authors state:
  • Residual confounding by smoking could not be ruled out, possibly more so among the lowest educated
  • Some lung carcinogens were not accounted for because no data were available, so the contribution of occupational exposures may be underestimated
  • The smoking measure did not account for the type of tobacco smoked
  • Job-exposure matrices produce non-differential misclassification, which could underestimate the asbestos and silica associations and their indirect effects
  • Recall bias could not be excluded for self-reported diesel motor exhaust exposure
  • Lack of statistical power may explain the results for men with a high school degree

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.

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