A case-control study of lung cancer nested in a cohort of European asphalt workers

Our plain-English summary of A case-control study of lung cancer nested in a cohort of European asphalt workers, by A. Olsson, H. Kromhout, M. Agostini, et al (Environmental Health Perspectives, 2010).

The study

• Authors: A. Olsson, H. Kromhout, M. Agostini, J. Hansen, C.F. Lassen, C. Johansen, K. Kjaerheim, S. Langård, I. Stücker, W. Ahrens, T. Behrens, M.L. Lindbohm, P. Heikkilä, D. Heederik, L. Portengen, J. Shaham, G. Ferro, F. de Vocht, I. Burstyn, P. Boffetta
• Journal: Environmental Health Perspectives
• Published: 2010;118(10):1418-24
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: We conducted a nested case-control study in a cohort of European asphalt workers in which an increase in lung cancer risk has been reported among workers exposed to airborne bitumen fume, although potential bias and confounding were not fully addressed.

Objective: We investigated the contribution of exposure to bitumen, other occupational agents, and tobacco smoking to the risk of lung cancer among asphalt workers.

Methods: Cases were cohort members in Denmark, Finland, France, Germany, the Netherlands, Norway, and Israel who had died of lung cancer between 1980 and the end of follow-up (2002-2005). Controls were individually matched in a 3:1 ratio to cases on year of birth and country. We derived exposure estimates for bitumen fume and condensate, organic vapor, and polycyclic aromatic hydrocarbons, as well as for asbestos, crystalline silica, diesel motor exhaust, and coal tar. Odds ratios (ORs) were calculated for ever-exposure, duration, average exposure, and cumulative exposure after adjusting for tobacco smoking and exposure to coal tar.

Results: A total of 433 cases and 1,253 controls were included in the analysis. The OR was 1.12 [95% confidence interval (CI), 0.84-1.49] for inhalation exposure to bitumen fume and 1.17 (95% CI, 0.88-1.56) for dermal exposure to bitumen condensate. No significant trend was observed between lung cancer risk and duration, average exposure, or cumulative exposure to bitumen fume or condensate.

Conclusions: We found no consistent evidence of an association between indicators of either inhalation or dermal exposure to bitumen and lung cancer risk. A sizable proportion of the excess mortality from lung cancer relative to the general population observed in the earlier cohort phase is likely attributable to high tobacco consumption and possibly to coal tar exposure, whereas other occupational agents do not appear to play an important role.

In plain English

This case-control study was nested within a cohort of male asphalt workers in Denmark, Finland, France, Germany, Israel, the Netherlands and Norway. Cases had died of lung cancer from 1980 to the end of follow-up (2002 to 2005), plus registry-identified cases in four countries. Controls were matched on birth year and country. The analysis included 433 cases and 1,253 control entries (1,131 interviewed controls, some used more than once). Compared with never-exposed workers, the lung cancer odds ratio for ever-exposed workers was 1.12 (95% CI 0.84 to 1.49) for inhaled bitumen fume and 1.17 (0.88 to 1.56) for skin contact with bitumen condensate. There was no significant trend by duration or amount. Asbestos, crystalline silica and diesel exhaust showed no association; an association with cumulative coal tar exposure was suggested. The authors concluded there was no consistent evidence linking bitumen to lung cancer. They judged that much of the earlier cohort's excess lung cancer deaths relative to the general population was likely due to heavy smoking and possibly coal tar. They described their assessment of non-bitumen agents as rather crude.

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: Nested case-control study within an existing cohort of European asphalt workers. Cases were deaths from lung cancer plus incident cases found through cancer registries in Denmark, Finland, Norway and Israel. Controls were matched to cases on birth year and country.
• Who was studied: Study base: 38,296 male asphalt-industry workers under 75 years of age in Denmark, Finland, France, Germany, the Netherlands, Norway and Israel. All had at least two full seasons of employment and were alive and cancer-free on 1 January 1980. The analysis included 433 lung cancer cases and 1,253 control entries, drawn from 1,131 interviewed controls; some controls were matched to more than one case. Follow-up ended between December 2002 (France) and June 2005 (Finland).
• Exposure: Semiquantitative estimates of inhalation exposure to bitumen fume, organic vapor and polycyclic aromatic hydrocarbons (PAHs), and of skin (dermal) exposure to bitumen condensate. Exposure to asbestos, crystalline silica, diesel motor exhaust and coal tar was scored (no, low, high) using job-exposure matrices. Smoking history was taken from interviews.
• Main results:
  • Participation: 436 cases were identified and agreed to be interviewed; 3 were excluded because no controls could be identified, leaving 433. Of the controls, 1,131 were interviewed. Because 184 controls were matched to more than one case, 1,253 control entries were included in the analysis.
  • Odds ratio for lung cancer, ever versus never exposed: 1.12 (95% CI 0.84 to 1.49) for inhalation exposure to bitumen fume, and 1.17 (95% CI 0.88 to 1.56) for dermal exposure to bitumen condensate.
  • No significant trend in lung cancer risk with duration, average exposure or cumulative exposure to bitumen fume or condensate.
  • Exposure to asbestos, crystalline silica and diesel motor exhaust showed no association with lung cancer risk. Detailed results are in a supplemental table not included in this text.
  • Ever-exposure to asbestos was assigned to 307 of 433 cases (70.9%) and 922 of 1,253 controls (73.6%).
  • An association was suggested between lung cancer and cumulative exposure to coal tar and, to a lesser extent, duration of exposure. In the highest cumulative coal tar category (16.89 to 196.48 unit-years; 54 cases, 100 controls), the OR was 1.60 (95% CI 1.09 to 2.36); the test for linear trend gave p = 0.07.
  • Smoking was strongly linked to lung cancer. Only 8 cases (1.8%) were never smokers, compared with 16.4% of controls. The OR was 6.12 (95% CI 2.92 to 12.81) for ex-smokers and 15.98 (95% CI 7.72 to 33.06) for current smokers.
  • Smokers were more common among controls than in national survey data. The estimated confounding ORs for smoking were 1.07 (Netherlands) to 1.28 (Denmark and Finland).
  • The authors judged that a sizable proportion of the excess lung cancer mortality seen in the earlier cohort phase, compared with the general population, is likely attributable to high tobacco consumption and possibly to coal tar exposure. They judged that other occupational agents do not appear to play an important role.
• The authors' conclusion: The authors concluded that they found no consistent evidence of an association between inhalation or dermal exposure to bitumen and lung cancer risk.
• Limitations the authors state:
  • Assessment of exposure to agents other than bitumen (including asbestos) was rather crude.
  • Co-exposures were so common that the study had limited power to detect small effects. For example, with 95% of controls exposed to diesel exhaust, power to detect an OR of 1.5 was about 25%.
  • Response rates were low in some countries, for example among controls in the Netherlands.
  • The results reflect exposure conditions of recent decades, when bitumen fume levels had decreased.
  • Chance remains a plausible explanation for the slight increases in some ORs.
  • The study may have failed to detect weak exposure-response associations.
  • The confounding ORs comparing smoking in controls with national surveys should be interpreted only qualitatively.

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: Case-Control Study, Lung Cancer, nested case-control study, Confounding, Crystalline, Odds Ratio, Cumulative Exposure, confidence interval.

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• Carcinoma of the pharynx and tonsils in an occupational cohort of asphalt workers — F. Zanardi, R. Salvarani, et al. (2013)
• Simulation tests to assess occupational exposure to airborne asbestos from artificially weathered asphalt-based roofing products — P. Sheehan, F. Mowat, et al. (2010)
• A review of changes in composition of hot mix asphalt in the United States — D.J. Mundt, K.M. Marano, et al. (2009)
• Prediagnostic detection of mesothelioma by circulating calretinin and mesothelin - a case-control comparison nested into a prospective cohort of asbestos-exposed workers — G. Johnen, K. Burek, et al. (2018)

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