Chronological trends in the causation of malignant mesothelioma: Fiber burden analysis of 619 cases over four decades

Our plain-English summary of Chronological trends in the causation of malignant mesothelioma: Fiber burden analysis of 619 cases over four decades, by V.L. Roggl, C.L. Green, B. Liu, et al (Environmental Research, 2023).

The study

• Authors: V.L. Roggl, C.L. Green, B. Liu, J.M. Carney, C.H. Glass, E.N. Pavlisko
• Journal: Environmental Research
• Published: 2023;230:114530
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma is a relatively rare malignancy with a strong association with prior asbestos exposure. A percentage of cases is not related to asbestos, and fiber analysis of lung tissue is a useful methodology for identifying idiopathic or spontaneous cases. We have performed fiber analyses in more than 600 cases of mesothelioma over the past four decades and were interested in looking for trends in terms of fiber types and concentrations as well as percentages of cases not related to asbestos. Demographic information was also considered including patient age, gender, and tumor location (pleural vs. peritoneal). The histologic pattern of the tumor and the presence or absence of pleural plaques or asbestosis were noted. Fiber analysis was performed in 619 cases, using the sodium hypochlorite technique for digestion of lung tissue samples. Asbestos bodies were counted by light microscopy (LM) and coated and uncoated fibers by scanning electron microscopy (EM). The results were stratified over four decades. Trends that were observed included increasing patient age, increasing percentage of women, increasing percentage of peritoneal cases, and increasing percentage of epithelial histological type. There was a decreasing trend in the percentage of patients with concomitant asbestosis (p < 0.001). The percentage of cases with an elevated lung asbestos content decreased from 90.5% in the 1980s to 54.1% in the 2010s (p < 0.001). This trend also held when the analysis was limited to 490 cases of pleural mesothelioma in men (91.8% in the 1980s vs. 65.1% in the 2010s). There was a decrease in the median asbestos body count by LM from 1390 asbestos bodies per gram of wet lung in the 1980s to 38 AB/gm in the 2010s. Similar trends were observed for each of the asbestos fiber types as detected by EM. We conclude that there has been a progressive decrease in lung fiber content of mesothelioma patients during the past four decades, with an increasing percentage of cases not related to asbestos and an increase in median patient age.

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In plain English

The authors reviewed 619 cases of histologically confirmed malignant mesothelioma whose lung tissue had been analyzed for asbestos in their laboratory from the 1980s through the 2010s. Most cases (86%) were referrals from asbestos litigation. Asbestos bodies were counted by light microscopy and six asbestos fiber types by scanning electron microscopy. Results were compared with 20 control cases with normal lungs at autopsy. The share of cases with lung asbestos content above the control range fell from 90.5% in the 1980s to 54.1% in the 2010s. Among 490 men with pleural mesothelioma it fell from 91.8% to 65.1%. Asbestosis alongside the mesothelioma fell from 12.5% to 0%. Among cases where asbestos bodies were found, the median count fell from 1,390 to 38 per gram of wet lung. Amosite, crocidolite, tremolite and actinolite levels also declined. Median age rose from 59 to 67, and the proportions of women, peritoneal cases and epithelial tumors rose. The authors concluded that lung asbestos content steadily decreased, with a rising proportion of cases not asbestos related. They noted that litigation cases may not represent all US cases.

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: Retrospective review of a single laboratory's database of mesothelioma cases with lung fiber burden analysis (case series), stratified by decade, with regression analysis of trends
• Who was studied: 619 histologically confirmed malignant mesothelioma cases analyzed at the authors' laboratory (Duke University): 74 in the 1980s, 212 in the 1990s, 211 in the 2000s, 122 in the 2010s. 86% were medical-legal referrals in asbestos litigation (41% from plaintiff attorneys, 45% from defendants) and 14% were consultations from other pathologists. A subgroup of 490 men with pleural mesothelioma was analyzed separately.
• Exposure: Lung tissue asbestos content. Asbestos bodies per gram of wet lung were counted by light microscopy. Amosite, crocidolite, tremolite, actinolite, anthophyllite and chrysotile fibers 5 μm or longer were counted by scanning electron microscopy. Results were compared with 20 control cases. A case counted as elevated if any of five parameters exceeded the control range. Occupational and non-occupational exposure categories were also tabulated.
• Main results:
  • Percentage of all cases with elevated lung asbestos content compared with controls: 90.5% (1980s), 89.2% (1990s), 79.6% (2000s), 54.1% (2010s). Odds of elevated content per decade: OR 0.43 (95% CI 0.33-0.54), p<0.001.
  • Among 490 men with pleural mesothelioma, the percentage with elevated lung asbestos content was 91.8% (1980s), 93.1% (1990s), 84.6% (2000s) and 65.1% (2010s).
  • Percentage of all cases with asbestosis: 12.5% (1980s), 8.6% (1990s), 5.0% (2000s), 0% (2010s). OR per decade 0.47 (95% CI 0.32-0.70), p<0.001.
  • The percentage of all cases with pleural plaques stayed fairly constant: 50.0% (1980s), 55.4% (1990s), 61.4% (2000s), 48.5% (2010s).
  • Median asbestos body count by light microscopy, among cases where asbestos bodies were detected, fell from 1,390 per gram of wet lung in the 1980s to 38 in the 2010s.
  • Levels of asbestos bodies and of amosite, crocidolite, tremolite and actinolite fibers decreased over time. The geometric mean ratios per decade were 0.39 for asbestos bodies, 0.44 for amosite, 0.52 for crocidolite, 0.68 for tremolite and 0.69 for actinolite. The p value was less than 0.001 for all except actinolite, where p was 0.004.
  • The percentage of cases with elevated crocidolite increased over the first three decades and then decreased in the fourth. Chrysotile was elevated in one in 5 cases in the 1980s and in fewer than 10% thereafter.
  • Median age of all cases rose from 59 (1980s) to 67 (2010s), an average increase of 2.07 years per decade (95% CI 1.08-3.06). Over the same period, men fell from 89.2% to 76.2% of cases and pleural cases from 94.5% to 90.2%. Epithelial histology rose from 31.0% to 52.1%.
  • The shipbuilding industry dominated exposure categories for the first three decades. US Navy and merchant marine exposures led in the 2010s. Electricians became the leading occupational category in the 2010s. Among women, household contact with asbestos workers was the primary mode of exposure.
• The authors' conclusion: The authors concluded that the asbestos fiber content of lung tissue in these mesothelioma cases steadily decreased over four decades. Over the same period, the relative proportion of cases not asbestos related increased, median age rose, the percentage of epithelial tumors rose, and concomitant asbestosis decreased to nearly none.
• Limitations the authors state:
  • 86% of cases came from asbestos litigation and may or may not be representative of all cases in the United States.
  • The trends would be less applicable to other countries with different timelines for workplace exposure limits, or none.

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: Causation, Mesothelioma, Fiber Burden Analysis, Asbestos Exposure, Idiopathic, Pleural Plaques, Asbestos Bodies, Scanning Electron Microscopy (SEM).

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• Diffuse malignant pleural mesothelioma in an urban hospital: clinical spectrum and trend in incidence over time — K.E. Shepherd, L.C. Oliver, et al. (1989)
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