Pleural plaques and asbestos-associated malignancy

Our plain-English summary of Pleural plaques and asbestos-associated malignancy, by P. Harber, Z. Mohsenifar, A. Oren, et al (Journal of Occupational Medicine., 1987).

The study

• Authors: P. Harber, Z. Mohsenifar, A. Oren, M. Lew
• Journal: Journal of Occupational Medicine.
• Published: 1987;29(8):641-4
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000320).

In plain English

This nested case-control study asked whether pleural plaques seen on chest radiographs signal a higher risk of later asbestos-associated cancer, apart from the effect of asbestos exposure itself. The starting group was 1,500 asbestos-exposed workers examined between 1979 and 1983 at three University of California, Los Angeles medical centers. Most had worked in shipyards, and most had been referred after filing compensation claims. Their median time working with asbestos was 24 years. At follow-up, an average of 30 months later, cancer information was obtained for 726 of them. Sixteen had developed an asbestos-associated malignancy, 13 of them bronchogenic carcinoma. Each was matched to one cancer-free man of the same race, smoking status and hospital, with similar age, exposure duration and pack-years. Two readers who did not know which men had cancer scored the earlier radiographs using several methods. No statistically significant differences were found, and there was no suggestion of a strong trend. The authors concluded that plaques per se do not appear causally related to later cancer. They acknowledged the small sample size and the lack of data on exposure intensity.

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 a cohort of asbestos-exposed workers, with one individually matched control per patient
• Who was studied: 1,500 asbestos-exposed workers examined from 1979 to 1983 at three University of California, Los Angeles medical centers (Center for Health Sciences, Cedars-Sinai, Harbor-UCLA). Most had been referred after filing a compensation claim for asbestos-related lung disease. Cancer status was obtained for 726. The analysis included 16 male patients with an asbestos-associated malignancy and 16 matched male controls known to be free of cancer.
• Exposure: Occupational asbestos exposure, mostly in shipyard new construction and refitting work. Median duration of work with asbestos exposure was 24 years. No fiber counts were available, but the authors judged from work descriptions that exposure was heavy. Fiber type is not stated.
• Main results:
  • Sixteen cases of asbestos-associated malignancy were identified. Thirteen were bronchogenic carcinoma; the others were colon, kidney and throat cancers.
  • Age, smoking history and duration of asbestos exposure were comparable between patients and controls.
  • Across all radiograph reading methods and statistical tests, there were no statistically significant differences between patients and controls in pleural plaque findings.
  • The authors reported no suggestion of a strong trend toward an association between pleural plaque and later malignancy.
  • Power estimates for 16 pairs, sign test: there was a 92% probability of finding a difference if 80% of patients' radiographs showed more plaque-like findings than their controls' radiographs, and an 81% chance if the true probability was .75.
  • Power estimates for the 12-point plaque score: a mean difference of 2 points between patients and controls would be detected with 60% likelihood, and a difference of 6 points with 81% power.
• The authors' conclusion: The authors concluded that plaques per se do not appear to be causally related to later cancer, and that any apparent association is a consequence of both being linked to asbestos exposure. They stated they do not believe the presence or absence of plaques should be used to allocate cancer screening resources among similarly exposed asbestos workers.
• Limitations the authors state:
  • The sample size for the statistical analysis was relatively small, which lowers statistical power. The authors stated that this does not bias the mean result.
  • Information on the intensity of asbestos exposure, such as fiber counts from personal sampling, was not available. The authors considered it unlikely that this explains the finding of no association.
  • Only one control per patient was selected. The authors noted that more controls would have increased statistical power, but those controls would have been less comparable to the patients.
  • The authors noted in advance that performing multiple analyses increased the chance of finding a 'statistically significant' result.

Topics

Medical terms in this study, explained in our Lexicon: Pleural Plaques.

Related studies

• Obstructive airway disease as a risk factor for asbestos-associated malignancy — P. Harber, A. Oren, et al. (1986)
• Refractory ceramic fiber exposure and pleural plaques — J. Lockey, G. Lemasters, et al. (1996)
• Multiple pleural plaques. II — H.C. Anton (1968)
• Pleural plaques, asbestos exposure, and asbestos bodies in bronchoalveolar lavage fluid — E. Orlowski, J.C. Pairon, et al. (1994)
• Gastrointestinal carcinoma and occurrence of pleural plaques on pulmonary X-ray — G. Hillerdal (1980)
• Value of the lateral view in diagnosing pleural plaques — G. Hillerdal (1986)

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