Is lung cancer associated with asbestos exposure when there are no small opacities on the chest radiograph?

Our plain-English summary of Is lung cancer associated with asbestos exposure when there are no small opacities on the chest radiograph?, by P. Wilkinson, D.M. Hansell, J. Janssens, et al (Lancet, 1995).

The study

• Authors: P. Wilkinson, D.M. Hansell, J. Janssens, M. Rubens, R.M. Rudd, A.N. Taylor, C. McDonald
• Journal: Lancet
• Published: 1995;345(8957):1074-8
• Cited by: 67 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This study was designed to test the hypothesis that the risk of lung cancer from asbestos exposure is confined to persons with radiographic evidence of pulmonary fibrosis. Occupational and smoking histories were obtained from 271 patients with a confirmed diagnosis of primary lung cancer and 678 referents (279 with other respiratory disease and 399 with cardiac disease). Histories were reviewed blind to assess the timing, duration, and probability of exposure to asbestos. To allow for a lag between asbestos exposure and the development of lung cancer, subjects were classified by the time they had spent in an occupation entailing definite or probable exposure more than 15 years before diagnosis. The presence and extent of fibrosis was assessed blindly from chest radiographs by three readers and scored for small opacities with the ILO 1989 International Classification of Radiographs of the Pneumoconioses. 93 (34.3%) cases had worked in an occupation with definite or probable asbestos exposure compared with 176 (25.8%) referents (crude odds ratio for lung cancer 1.49, 95% CI 1.09-2.04). After adjustment for age, sex, smoking history, and area of referral, the odds ratio (95% CI) was 2.03 (1.00-4.13) in the subgroup of 211 with a median ILO score for small parenchymal opacities of 1/0 or more, and 1.56 (1.02-2.39) in the 738 with a score of 0/1 or less (ie, those without radiological evidence of pulmonary fibrosis). These results suggest that asbestos is associated with lung cancer even in the absence of radiologically apparent pulmonary fibrosis.

In plain English

This hospital-based case-referent study tested whether asbestos-linked lung cancer risk is confined to people whose chest X-rays show lung scarring (fibrosis). At the London Chest Hospital between September 1992 and March 1993, the authors studied 271 patients with primary lung cancer and 678 referents with other respiratory or heart disease. Jobs held more than 15 years before diagnosis were classified, without knowing the diagnosis, by probability of asbestos exposure. Three readers scored the X-rays for small opacities using the ILO system. Overall, 34.3% of cases and 25.8% of referents had worked in jobs with definite or probable exposure. After adjusting for age, sex, smoking and referral type, the odds ratio for lung cancer was 2.03 (95% CI 1.00 to 4.13) in the 211 patients with opacity scores of 1/0 or more. It was 1.56 (1.02 to 2.39) in the 738 with scores of 0/1 or less (no X-ray sign of fibrosis). The authors concluded that their results do not suggest X-ray evidence of fibrosis is a prerequisite for asbestos-related lung cancer. They noted that an X-ray without small opacities does not rule out microscopic fibrosis.

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: Hospital-based case-referent (case-control) study
• Who was studied: Adult admissions to the London Chest Hospital, September 1992 to March 1993: 271 patients with confirmed primary lung cancer (cases) and 678 referents (279 with other respiratory disease, 399 with cardiac disease)
• Exposure: Work in occupations classified as entailing definite or probable asbestos exposure, counted only for jobs more than 15 years before diagnosis. Jobs were assigned to a list of 31 occupations taken from an earlier mesothelioma study. Fiber types were not specified.
• Main results:
  • In the whole study group, 93 (34.3%) cases and 176 (25.8%) referents had worked in an occupation with definite or probable asbestos exposure (crude odds ratio 1.49, 95% CI 1.09-2.04)
  • For any relevant job versus none, the odds ratio adjusted for age, sex, smoking and type of referral was 1.66 (1.15-2.38). With respiratory referents only it was 2.02 (1.26-3.24). With cardiac referents only it was 1.44 (0.96-2.16).
  • Adjusted odds ratio was 2.03 (1.00-4.13) in the 211 patients with a median ILO small-opacity score of 1/0 or more. It was 1.56 (1.02-2.39) in the 738 with a score of 0/1 or less, the group without radiological evidence of fibrosis.
  • In the 655 patients with a median ILO score of 0/0 or less, the adjusted odds ratio was 1.48, with a lower confidence limit of 0.93; the upper limit is garbled in the scan. Separately, the odds ratio was 2.09 (1.12-3.89) with respiratory referents and 1.35 (0.82-2.22) with cardiac referents.
  • In patients without parenchymal opacities, the authors described some, albeit weak, evidence that risk rose with duration of exposure
  • Only 121 (44.9%) of the 269 patients classified as exposed from their occupation reported working with asbestos. In the subgroup with ILO scores of 0/1 or less, the adjusted odds ratio for self-reported exposure was 1.19 (0.73-1.91).
  • Exposure only within the 15 years before diagnosis had an odds ratio of 1.11 (0.34-3.59) in the whole study group
• The authors' conclusion: The authors concluded that their results do not suggest that radiological evidence of fibrosis is a prerequisite for asbestos-related lung cancer
• Limitations the authors state:
  • As in most case-referent studies, not all bias could be eliminated
  • Blacking out parts of the X-ray to hide the diagnosis may sometimes have hidden an area of fibrosis
  • Absence of small opacities on the chest X-ray does not exclude microscopic fibrosis
  • Citing other work, the authors noted that chest X-rays detect fibrosis in only about 80% of cases with histological evidence
  • The independent effect of recent exposure could not be determined precisely
  • Job classification was likely to have caused random misclassification of exposure, which the authors said would bias results toward the null

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Asbestos Exposure, Chest X-Ray, Pulmonary Fibrosis, Fibrosis, Odds Ratio.

Related studies

• Progression of small, irregular opacities in chest radiographs of former asbestos workers — B. Świątkowska, W. Sobala, et al. (2012)
• Lung function and chest radiograph abnormalities among construction insulators — S.M. Kennedy, S. Vedal, et al. (1991)
• Risk and significance of chest radiograph and pulmonary function abnormalities in an elderly cohort of former nuclear weapons workers — M.A. Mikulski, P.G. Hartley, et al. (2011)
• Cigarette smoke, asbestos, and small irregular opacities — W. Weiss (1984)
• Cigarette smoking and small irregular opacities — W. Weiss (1991)
• The effect of cigarette smoking on the detection of small radiographic opacities in inorganic dust diseases — P.D. Blanc, G. Gamsu (1988)

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