Asbestos fibreyears and lung cancer: a two phase case-control study with expert exposure assessment

Our plain-English summary of Asbestos fibreyears and lung cancer: a two phase case-control study with expert exposure assessment, by H. Pohlabeln, P. Wild, W. Schill, et al (Occupational and Environmental Medicine, 2002).

The study

• Authors: H. Pohlabeln, P. Wild, W. Schill, W. Ahrens, I. Jahn, U. Bolm-Audorff, K.H. Jöckel
• Journal: Occupational and Environmental Medicine
• Published: 2002;59(6):410-4
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: To assess the cumulative effect of asbestos on lung cancer risk where the exposure is assessed by an expert rating.

Methods: 1678 male cases and controls were enrolled in a population based matched case-control study, focused on occupational risk factors, carried out in West Germany. The exposure to asbestos was computed as lifelong working hours. For a validation subsample of 164 matched pairs from this study the intensity of asbestos exposure was further assessed by a panel of experts in order to obtain an estimate of the cumulative exposure on a time by intensity scale (fibreyears). The information on duration of asbestos exposure in the original study was combined with the fibreyears following the two phase case control study paradigm.

Results: The number of exposed subjects in the validation subsample was 75 cases and 71 controls. The percentage of subjects with a cumulative exposure < or =1, 1 to < or =10, and >10 fibreyears was 16%, 15%, and 15% for the cases and 18%, 16%, and 9% respectively for the controls. The smoking adjusted odds ratios for the fibreyears based on an unconditional logistic regression were 0.81, 1.02, and 1.60 respectively with increasing exposure categories (not significant). The coefficient (beta) for a log transformed trend was 1.156. Applying the two phase paradigm, these odds ratios became 0.86, 1.33, and 1.94; the latter reached significance and the beta coefficient was 1.178.

Conclusions: The two phase paradigm allowed us to obtain a more precise estimate of the effect of asbestos on lung cancer. Results are consistent with a doubling of the lung cancer risk with 25 fibreyears asbestos exposure.

In plain English

This German study asked whether lung cancer risk rose with cumulative asbestos exposure measured in 'fibreyears'. It was a population based matched case–control study of 839 men with lung cancer from hospitals in Bremen and Frankfurt/Main (1988 to 1993) and 839 male controls drawn at random from residence registries. For 164 cases and their 164 controls from Bremen, two industrial hygiene experts estimated cumulative exposure in fibreyears without knowing who had cancer. The study did not report results by asbestos fiber type. In the full study, men in the highest category of lifelong hours of exposure had a smoking adjusted odds ratio of 1.47 (95% CI 1.04 to 2.08). In the subsample alone, the odds ratio for more than 10 fibreyears versus none was 1.60 (95% CI 0.75 to 3.40), not statistically significant. Combining both data sets in a 'two phase' analysis gave 1.94 (95% CI 1.10 to 3.43). At 25 fibreyears the model estimated 1.71 (95% CI 1.18 to 2.46). The authors concluded the results were consistent with a doubling of lung cancer risk at 25 fibreyears. They noted that expert estimates are imprecise without measurements.

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 matched case–control study, with controls randomly drawn from residence registries. Exposure was expert-rated in a validation subsample, and the data were analysed as a two phase case–control study.
• Who was studied: 839 male lung cancer cases and 839 male controls matched on age and region. Cases came from hospitals in Bremen (1988 to 1993) and Frankfurt/Main (1989 to March 1990), West Germany. Controls came from residence registries. The validation subsample was 164 cases and their 164 controls, all from the Bremen hospital recruitment in 1991 and 1992.
• Exposure: Occupational asbestos exposure; the study did not distinguish fiber types. For all subjects it was measured as lifelong hours of exposure from supplementary questionnaires. In the subsample, experts estimated fibres/ml for each job phase and multiplied by duration to give cumulative fibreyears.
• Main results:
  • In the full study (conditional regression with smoking in the model), men with more than 5280 lifelong hours of asbestos exposure (124 cases, 84 controls) had an OR of 1.47 (95% CI 1.04 to 2.08) compared with non-exposed men.
  • In the validation subsample, taking the expert assessment as the standard, the questionnaire-based exposure measure had a sensitivity of 93% and a specificity of 95%.
  • In the validation subsample alone (unconditional, smoking adjusted), the ORs were 0.81, 1.02 and 1.60 for the three rising fibreyear categories compared with non-exposed men. The only OR substantially above one was 1.60 (95% CI 0.75 to 3.40) for more than 10 fibreyears, and it was not statistically significant.
  • In the two phase analysis combining both data sets, the OR for 10 or more fibreyears was 1.94 (95% CI 1.10 to 3.43), the only category significantly above 1. The other ORs were 0.86 (0.55 to 1.33) for 0 to under 1 fibreyear and 1.33 (0.80 to 2.23) for 1 to under 10.
  • At 25 fibreyears, the basis of the German compensation scheme, the two phase log-fibreyear model gave an OR of 1.71 (95% CI 1.18 to 2.46).
  • A separate category for more than 25 fibreyears gave an OR of 1.73 (95% CI 0.85 to 3.53).
• The authors' conclusion: The authors concluded that the two phase method gave a more precise estimate than the validation sample alone. They also concluded that the results are consistent with a doubling of lung cancer risk with 25 fibreyears of asbestos exposure.
• Limitations the authors state:
  • The expert estimates of cumulative dose are necessarily imprecise because no measurements were available.
  • The study was not originally designed as a two phase study.
  • Smoking could be used in only two categories for the two phase stratification, because no non-smoking case fell in the highest asbestos duration category.
  • The two phase analysis cannot account for the matching of cases and controls.
  • The way the validation sample was chosen was not optimal for efficiency.

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, Asbestos Exposure, Cumulative Exposure, Odds Ratio.

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