Occupational risk factors have to be considered in the definition of high-risk lung cancer populations

Our plain-English summary of Occupational risk factors have to be considered in the definition of high-risk lung cancer populations, by P. Wild, M. Gonzalez, E. Bourgkard, et al (British Journal of Cancer, 2012).

The study

• Authors: P. Wild, M. Gonzalez, E. Bourgkard, N. Courouble, C. Clément-Duchêne, Y. Martinet, J. Févotte, C. Paris
• Journal: British Journal of Cancer
• Published: 2012;106(7):1346-52
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The aim of this study was to compute attributable fractions (AF) to occupational factors in an area in North-Eastern France with high lung cancer rates and a past of mining and steel industry.

Methods: A population-based case-control study among males aged 40-79 was conducted, including confirmed primary lung cancer cases from all hospitals of the study region. Controls were stratified by broad age-classes, district and socioeconomic classes. Detailed occupational and personal risk factors were obtained in face-to-face interviews. Cumulative occupational exposure indices were obtained from the questionnaires. Attributable fractions were computed from multiple unconditional logistic regression models.

Results: A total of 246 cases and 531 controls were included. The odds ratios (ORs) adjusted on cumulative smoking and family history of lung cancer increased significantly with the cumulative exposure indices to asbestos, polycyclic aromatic hydrocarbons and crystalline silica, and with exposure to diesel motor exhaust. The AF for occupational factors exceeded 50%, the most important contributor being crystalline silica and asbestos.

Conclusion: These AFs are higher than most published figures. This can be because of the highly industrialised area or methods for exposure assessments. Occupational factors are important risk factors and should not be forgotten when defining high-risk lung cancer populations.

In plain English

This population-based case-control study examined lung cancer in men aged 40 to 79 in four districts of northern Lorraine, France, an area with a past of mining and steel industry. From 2006 to 2010, 246 men with confirmed lung cancer and 531 comparison men chosen by random telephone dialling were interviewed at home. Detailed questionnaires were used to estimate lifetime workplace exposure to asbestos (fiber type not specified), polycyclic aromatic hydrocarbons (PAH), crystalline silica, diesel exhaust and other agents. About 52% of comparison men had been exposed to asbestos. After adjusting for smoking and other factors, lung cancer odds rose with cumulative asbestos, PAH and silica exposure, and were higher with diesel exhaust exposure. Men in the highest quarter of asbestos exposure had an odds ratio of 2.70 (95% CI 1.50 to 4.87) versus unexposed men. An estimated 56% (41 to 67%) of the lung cancers were attributed to all workplace exposures together, including 22% (9 to 34%) to asbestos. The authors concluded that occupational factors should be considered when defining high-risk groups. They noted a relatively small number of cases.

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, analysed with multiple unconditional logistic regression and attributable fractions
• Who was studied: 246 men with histologically confirmed primary lung cancer and 531 male controls, aged 40 to 79. The Methods word eligibility as between 40 and 80, and the oldest age class in Table 1 is 70 to 79. Controls were selected by random digit dialling and stratified by age class, district and socioeconomic class. All lived in four administrative districts of northern Lorraine, France (about 800,000 inhabitants), near the German and Luxembourg borders. Interviews ran from February 2006 to December 2010.
• Exposure: Lifetime occupational exposures estimated from job-specific and task-based questionnaires, with exposure levels assigned with industrial hygienists. Exposures included asbestos (15 task questions; cumulative index in years times fibers per ml; fiber type not specified), PAH, crystalline silica, diesel motor exhaust, man-made mineral fibers, refractory ceramic fibers, welding, iron mining and other agents.
• Main results:
  • About 52% of controls were exposed to asbestos. Non-exposed: 255 controls (48.0%) and 71 cases (28.9%).
  • Crude (unadjusted) odds ratios rose with cumulative exposure to asbestos, PAH and crystalline silica and exceeded three in the highest quartiles: 3.8 for asbestos, 3.2 for PAH and 3.1 for silica.
  • After adjustment for other occupational and non-occupational factors, only asbestos, crystalline silica, PAH and diesel motor exhaust were significant risk factors.
  • Asbestos, adjusted model with a continuous exposure variable: odds ratio 1.182 (95% CI 1.064, 1.313) per unit of log(fiber-years per ml + 1).
  • Asbestos, adjusted odds ratios by quartile versus non-exposed: Q1 1.30 (0.73, 2.30), Q2 1.60 (0.90, 2.83), Q3 1.67 (0.94, 2.94), Q4 2.70 (1.50, 4.87).
  • Fraction of lung cancers attributable to asbestos: 22% (9, 34%) in the continuous-exposure model and 31% (10, 47%) in the quartile model.
  • Crystalline silica: adjusted odds ratio 1.07 (1.011, 1.140) per unit of log exposure; attributable fraction 30% (6, 49%) in the continuous model.
  • PAH: adjusted odds ratio 1.166 (1.036, 1.312) per unit of log exposure; attributable fraction 11% (2, 20%) in the continuous model.
  • Diesel motor exhaust exposure: adjusted odds ratio 1.66 (1.11, 2.49); attributable fraction 15% (3, 25%).
  • Overall fraction of lung cancers attributable to occupational factors: 56% (41, 67%) in the continuous model and 52% (32, 66%) in the quartile model.
  • Refractory ceramic fibers, man-made mineral fibers, iron mining, stainless steel welding and other occupational exposures had no significant relation with lung cancer after adjustment.
  • No evidence was found of a specific effect of concomitant exposures.
  • According to the online appendix, about 10% of lung cancer cases in the study area are recognised as due to occupational factors. The authors noted this is much lower than the 50% attributable fraction.
• The authors' conclusion: The authors concluded that, at least in areas with hazardous industries, occupational lung cancers are not a thing of the past. They wrote that asbestos-related lung cancers may eventually fade following the ban, but prevention must be sustained for crystalline silica, PAH and diesel exhaust. They also concluded that occupational risk factors should be included alongside smoking in prediction models used to identify high-risk people, for example for CT screening.
• Limitations the authors state:
  • Relatively small number of cases, partly due to a less than optimal response rate in cases.
  • Controls were selected by random digit dialling.
  • Hospitals' participation in finding cases was unequal.
  • The diesel exhaust result is rather weak evidence because no cumulative exposure estimate could be made.
  • Exposure frequency could not be included in the crystalline silica index, which might have weakened the dose-effect relationship.
  • The exposure measures were sensitive and specific for asbestos but less so for PAH.
  • Other recognised occupational carcinogens did not reach significance, mostly because very few subjects were exposed.

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: Lung Cancer, Case-Control Study, Occupational Exposure, Odds Ratio, Cumulative Exposure, Crystalline.

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