Residual fibre lung burden among patients with pleural mesothelioma who have been occupationally exposed to asbestos

Our plain-English summary of Residual fibre lung burden among patients with pleural mesothelioma who have been occupationally exposed to asbestos, by E. Merler, A. Somigliana, P. Girardi, et al (Occupational and Environmental Medicine, 2017).

The study

• Authors: E. Merler, A. Somigliana, P. Girardi, P.G. Barbieri
• Journal: Occupational and Environmental Medicine
• Published: 2017;74(3):218-227
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: To evaluate the lungs asbestos fibres concentration in participants with malignant pleural mesothelioma (MPM) who have been occupationally exposed.

Methods: The lung samples were obtained from pleuropneumonectomies or autopsies of 271 male MPMs. The lung samples were examined through scanning electron microscopy. Retrospective assessment was used to assess for asbestos exposure. This study includes 248 MPMs with an occupational exposure defined as either 'definite' or 'probable' or 'possible'.

Results: The participants had finished working in asbestos exposure conditions more than 20 years ago (on average 26.1±11.0 years). The fibre burden resulted with a geometric mean equal to 2.0 (95% CI 1.6 to 2.4) million fibres per gram of dry lung tissue. The burden was higher among participants employed in asbestos textiles industry and in shipyards with insulation material, if compared with construction workers or non-asbestos textile workers or participants working in chemicals or as auto mechanics. 91.3% of MPMs had a detectable amount of amphibole fibres. A strong lung clearance capability was evident among workers exposed to chrysotile fibres. Owing to that, the 1997 Helsinki Criteria for occupational exposure were reached in <35% of cases among participant working in construction, in metallurgical industry, in chemical or textile industry and among those performing brake repair activities.

Conclusions: The MPM cases are now occurring in Italy in participants who ceased occupational asbestos exposure decades before the analysis. A large majority still shows a residual content of amphibole fibres, but given the lung clearance capability, attribution to occupational exposure cannot rely only on fibres detection.

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In plain English

This Italian study measured asbestos fibres left in the lungs of 271 people with definite malignant pleural mesothelioma classified as occupationally exposed. Lung tissue came from surgery or autopsy in North East Italy and was sent to a single laboratory between 2001 and 2014. It was examined by scanning electron microscopy. A cumulative exposure index based on work histories was available for 207 of the 271 cases. On average, 26.1 years had passed since the last job involving asbestos. The overall geometric mean was 2.0 million fibres per gram of dry lung tissue (95% confidence interval 1.6 to 2.4). Levels were highest in asbestos textile, asbestos cement and shipyard workers. They were lowest in brake repair, chemical, non-asbestos textile and building construction workers. Amphibole fibres were found in 88.6% of samples and chrysotile in 55.4%. Only 48.3% of cases met the 1997 Helsinki Criteria amphibole threshold. Estimated exposure correlated with amphibole levels. For chrysotile the correlation was weak and not statistically significant. The authors concluded that, because the lungs clear fibres, attribution to occupational exposure cannot rely only on fibre detection.

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: Descriptive study of lung fibre burden in mesothelioma cases from regional mesothelioma registries, combining scanning electron microscopy of lung tissue with a retrospective assessment of occupational asbestos exposure
• Who was studied: 271 'definite' malignant pleural mesothelioma cases classified as occupationally exposed (121 surgical samples, 150 autopsy samples; 248 men and 23 women; average age 68.4 years), drawn from 316 cases whose lung tissue was sent to a single laboratory in 2001 to 2014, mainly from North East Italy
• Exposure: Occupational asbestos exposure in job sectors including asbestos textile, asbestos cement, shipyards, industrial plant construction, railway carriages, insulation, foundry, building construction, chemical industry, non-asbestos textile and brake repair. Exposure was estimated as a Cumulative Exposure Index. Lung fibres were counted and identified as amosite, crocidolite, anthophyllite, chrysotile or tremolite.
• Main results:
  • The Cumulative Exposure Index, based on work histories, could be calculated for 207 of the 271 cases
  • Across all cases, the geometric mean fibre burden was 2.0 (95% CI 1.6 to 2.4) million fibres per gram of dry lung tissue
  • On average, participants had finished working in asbestos-exposed conditions 26.1 (SD 11.0) years before the analysis
  • The highest geometric means were among cases who worked in asbestos textile (22 Mff/g dt), asbestos cement production and installation (13.1) and shipbuilding and ship repair (5.4)
  • The lowest geometric means were among cases who worked in body shops and brake repair (0.6 Mff/g dt), chemicals production (0.8), non-asbestos textile industries (0.9) and building construction (1)
  • Cases with a 'certain' occupational exposure had a higher geometric mean (2.4 Mff/g dt) than those with 'probable' or 'possible' exposure (0.7 Mff/g dt), p less than 0.001
  • Amphibole fibres were detected in 88.6% of lung samples and chrysotile fibres in 55.4%. In 17 participants no commercial amphiboles were found, only chrysotile and/or tremolite.
  • In 9 participants (3.3% of the total) the fibre amount was below the detection limit, although all had been judged certainly exposed
  • Nine participants (2 of them women) had a fibre count above 100 Mff/g dt. They had worked in asbestos cement production, in shipyards and in recycling jute sacks that had contained asbestos.
  • Only 48.3% of cases met the 1997 Helsinki Criteria (amphiboles above 1 Mff/g dt). The share was 75% for railway carriage, asbestos cement and shipyard workers, and less than 20% for chemical industry, brake repair and non-asbestos textile workers.
  • If a lung clearance rate of 12% per year for amphibole fibres was applied, attribution rose from about 50% to 88.9%
  • The Cumulative Exposure Index correlated with total fibre burden (Spearman rho 0.57, p less than 0.01) and with amphibole fibres (rho 0.58, p less than 0.01). The correlation with chrysotile fibres was weak and not statistically significant (rho 0.14, p 0.19).
• The authors' conclusion: The authors concluded that pleural mesothelioma cases in Italy now occur in people whose occupational exposure ended decades earlier. Most still have residual amphibole fibres in the lung, but because of lung clearance, attribution to occupational exposure cannot rely only on fibre detection. They found agreement with the 2014 Helsinki proposition that a history of significant exposure will suffice for attribution.
• Limitations the authors state:
  • The cases were a specific sample, with a predominance of the epithelial subtype because surgery was performed mainly on that subtype
  • The higher fibre burden in autopsy samples suggests that autopsies were done when an occupational disease was suspected
  • The sample reflects only partially the range of activities in which asbestos was used
  • Chrysotile fibres may have been underestimated because retained chrysotile fibres can be smaller than the method could detect
  • Diagnoses of asbestosis and pleural plaques were not validated, and the histological diagnoses of mesothelioma were not reviewed
  • Estimates of exposure intensity were mainly based on values from the literature

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Scanning Electron Microscopy (SEM), Asbestos Exposure, Occupational Exposure, Asbestos Textiles, Amphibole Group, Chrysotile, Helsinki Criteria.

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