Lung asbestos content in lungs resected for primary lung cancer

Our plain-English summary of Lung asbestos content in lungs resected for primary lung cancer, by C.M. Wright, R.V. Bowman, M.E. Tan, et al (Journal of Thoracic Oncology, 2008).

The study

• Authors: C.M. Wright, R.V. Bowman, M.E. Tan, M.U. Martins, R.E. McLachlan, L.H. Passmore, M.N. Windsor, B.E. Clarke, E.E. Duhig, A.M. Mahar, K. Fong
• Journal: Journal of Thoracic Oncology
• Published: 2008;3(6):569-76
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: The majority of Australia's burden of lung cancer occurs in current or former tobacco smokers. To determine the possible contribution of asbestos exposure in Australians presenting with primary lung cancer, we measured lung asbestos content in cases resected consecutively at a single cardio-thoracic hospital.

Methods: Asbestos bodies were quantified by lung tissue digestion, filtration, and light microscopy, and were correlated with exposure questionnaires and clinicopathological features.

Results: We demonstrate high intrarater reproducibility and interrater reliability using these methods. In 463 patients with resected primary lung cancers, asbestos content ranged from 0 to 749 asbestos bodies per gram wet weight (AB/gww). Forty-eight percent of patients had no asbestos bodies identified. One-third had less than or equal to 20 AB/gww (a level previously found to be consistent with urban dwelling). Nineteen percent had lung content in excess of this level. Only 20 cases had AB >100/gww, approximately equivalent to the Helsinki threshold for attribution of lung cancer to asbestos. Median asbestos body counts were higher in patients who reported previous asbestos exposure than in those who reported no exposure. A subgroup of cases gave detailed exposure histories that did not predict presence or absence of asbestos bodies in men or women. In cases with cumulative tobacco exposure less than 20 pack-years, asbestos body counts exceeding 20 AB/gww were overrepresented.

Conclusions: We found that the majority of patients with primary lung cancer at a single Australian center have detectable asbestos in resected lung tissue, but fiber burdens are generally low. The contributory role of this low-level asbestos exposure in causing lung cancer remains uncertain.

In plain English

The authors counted asbestos bodies (coated fibers) by light microscopy in lung tissue taken away from the tumor in 463 consecutive patients (317 men, 146 women). All had primary lung cancer removed at The Prince Charles Hospital, Australia, between 2000 and 2006. The authors compared the counts with patients' own reports of past exposure. Counts were highly reproducible between readers. No asbestos bodies were found in 223 patients (48%). Another 152 (33%) had up to 20 per gram of wet lung, a level previously linked to urban living, and 88 (19%) had 20 or more. Twenty patients (4.3%) had over 100 per gram, and only two exceeded 500, the authors' approximation of the Helsinki threshold for attributing lung cancer to asbestos. Patients reporting past exposure had a higher median count than those reporting none (8.4 versus 0), with considerable overlap. Counts above 20 were over-represented among patients with under 20 pack-years of smoking. The authors concluded asbestos is not likely a major causal contributor in most of these cases, though how low-level exposure interacts with smoking remains unknown. They noted their method likely underestimates total fiber content.

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: Consecutive case series (cross-sectional measurement) of lung asbestos body counts in patients having surgery for primary lung cancer, compared with self-reported exposure and clinical features
• Who was studied: 463 consecutive patients (146 women, 317 men) with primary lung cancer resected at The Prince Charles Hospital, Chermside, Australia, between 2000 and 2006
• Exposure: Asbestos bodies counted by light microscopy per gram wet weight of lung tissue, plus self-reported asbestos exposure (yes, no or unsure; a subset completed a detailed questionnaire). Fiber type could not be identified. The authors state the counts mainly reflect amphibole exposure.
• Main results:
  • Agreement among three readers counting the same 60 lung samples was high (intraclass correlation 0.93, 95% CI 0.89 to 0.95)
  • Of the 463 patients, 88 (19%) had 20 or more asbestos bodies per gram wet weight, 152 (33%) had up to 20, and 223 (48%) had none
  • 20 patients (17 men, 3 women), 4.3% of the total, had more than 100 asbestos bodies per gram wet tissue, a range the authors linked to a high probability of exposure at work
  • Only two patients had more than 500 asbestos bodies per gram wet weight, the authors' approximation of the Helsinki threshold for causal attribution of lung cancer
  • Among the 348 patients who answered the exposure question, those reporting no exposure had a median of 0 asbestos bodies per gram (range 0 to 749). Those recalling past exposure had a median of 8.4 (range 0 to 524), p less than 0.0001. The two groups overlapped considerably.
  • Among men who completed the detailed questionnaire, 83% of those reporting occupational exposure had asbestos bodies (24/29). So did 39% of those reporting no exposure (12/31).
  • None of the 17 women with detailed questionnaires reported occupational exposure, yet 7 had asbestos bodies (4 with more than 20 per gram). Women and men had a similar distribution of counts.
  • Counts above 20 per gram were over-represented among patients with 0 or under 20 pack-years of smoking: 24 of 77, against 14.6 expected. Among those with more than 20 pack-years the figure was 64 of 386 (p 0.003).
  • No significant differences by demographic variables, lobe location, or tumor histologic subtype according to asbestos content
• The authors' conclusion: The authors concluded that retained asbestos burdens in this series were very low compared with burdens epidemiologically associated with increased lung cancer risk. In their view, asbestos is not likely to be a major causal contributor in the majority of cases, though how low-level asbestos exposure interacts with tobacco remains unknown.
• Limitations the authors state:
  • Light microscopy cannot detect short or thin fibers, so total lung fiber content is very likely underestimated
  • The method cannot identify fiber type, so retained chrysotile is not accurately assessed
  • Wet/dry lung weight ratios were not measured, so comparison with the Helsinki thresholds is an approximation
  • The method is not comparable with electron microscopy methods
  • No systematic corroborating evidence of exposure, such as detailed occupational histories or pleural plaques on CT, for the cohort
  • Fiber content can vary up to 10-fold between regions of the same lung
  • Residential information was not available to explore possible environmental exposure in women

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, Asbestos Exposure, Asbestos Bodies, Tissue Digestion, Attribution, Asbestos Body Formation, Fiber Burden.

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