Twenty-five years of fiber analysis: what have we learned?

Our plain-English summary of Twenty-five years of fiber analysis: what have we learned?, by V.L. Roggli, R.T. Vollmer (Human Pathology, 2008).

The study

• Authors: V.L. Roggli, R.T. Vollmer
• Journal: Human Pathology
• Published: 2008;39(3):307-15
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos exposure has resulted in a variety of diseases, including asbestosis, carcinoma of the lung (LC), pleural plaques, and malignant mesothelioma (MM). We hypothesized that there have been significant changes in the mineral fiber content of lung tissue from individuals with these diseases over the past 25 years. Asbestos content was measured in lung tissue samples from 819 individuals using light microscopy (to measure asbestos body concentrations) and scanning electron microscopy (to measure types and concentrations of mineral fibers). Cases were divided chronologically according to those occurring in the first half (group 1) versus those occurring in the second half (group 2). The study included 419 cases of MM, 206 cases of asbestosis, and 340 cases of LC. The median asbestos body count (in asbestos bodies per gram) decreased from group 1 to group 2 for each disease: MM, 480 to 350; asbestosis, 24700 to 19200; and LC, 1600 to 174 (reference range, 0-20). A similar trend was observed for fiber counts by scanning electron microscopy. Amosite was the most frequently detected asbestos fiber type and decreased in frequency of detection and median concentration from group 1 to group 2. Crocidolite showed an increased detection frequency from group 1 to group 2 across all 3 disease categories. The decrease in asbestos body and amosite concentrations over time is consistent with the banning of asbestos from insulation products in 1972. The source for the increased detection of crocidolite was not identified and needs further investigation.

In plain English

Using a single Duke University laboratory's records, the authors reviewed lung tissue fiber analyses performed between August 1980 and August 2005 on cases of malignant mesothelioma (419), lung cancer (340) and asbestosis (206). Some asbestosis cases also had one of the cancers, and about 60% of cases were medical-legal referrals. Each disease group was split by date into an earlier and a later half. Median asbestos body counts per gram of wet lung fell from the earlier to the later half: mesothelioma 480 to 350, asbestosis 24700 to 19200 (not statistically significant), and lung cancer 1600 to 174, against a laboratory reference range of 0 to 20. Amosite was the most common fiber type, and both its detection rate and its median concentration fell. Crocidolite was detected more often in the later half in all three diseases, while chrysotile was detected less often. The authors concluded that the falls in asbestos body and amosite concentrations were consistent with the 1972 ban of asbestos from insulation products, and that the source of the more frequent crocidolite detection needs further investigation.

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 lung fiber burden case database, comparing earlier and later cases. Asbestos bodies were counted by light microscopy and fiber types and concentrations were measured by scanning electron microscopy (SEM).
• Who was studied: Cases with lung fiber burden analysis at the Duke University and Durham VA laboratory, Durham, NC, between August 1980 and August 2005. There were 419 malignant mesothelioma cases (209 in group 1, 210 in group 2; the methods section says 421), 340 lung cancer cases (170 and 170) and 206 asbestosis cases (103 and 103). Of the asbestosis cases, 54 also had mesothelioma and 91 had lung cancer. About 60% of cases were medical-legal referrals. Results were compared with 20 laboratory controls with no asbestos-related disease and no history of asbestos exposure.
• Exposure: Asbestos content of lung tissue: asbestos bodies, and fibers 5 μm or longer classified as amosite, crocidolite, tremolite, anthophyllite, actinolite or chrysotile. Exposure information was available for 679 cases. Shipbuilding and insulation were the leading industries, with pipe fitters/welders the leading occupation, and household contacts of asbestos workers also made up a share of cases.
• Main results:
  • Median asbestos body counts per gram fell from group 1 to group 2 in every disease: mesothelioma 480 to 350, asbestosis 24700 to 19200, lung cancer 1600 to 174 (reference range 0 to 20). The tables show the fall was statistically significant for mesothelioma (P = .006) and lung cancer (P = .0001), but not for asbestosis.
  • Mesothelioma cases with asbestos body counts above the reference range fell from 83% in group 1 to 74% in group 2. For lung cancer cases the figures were 86% and 69%. All asbestosis cases in both groups were above the reference range.
  • Amosite was the most common fiber type in all three diseases. Its detection fell from group 1 to group 2: mesothelioma 164 of 199 (82%) to 139 of 206 (67%); lung cancer 139 of 155 (90%) to 112 of 160 (70%); asbestosis 92 of 94 (98%) to 94 of 102 (92%). Its median concentration also fell.
  • Crocidolite was detected more often in group 2 in all three diseases: mesothelioma 46 cases (23%) to 87 (42%); asbestosis 22 (23%) to 51 (50%); lung cancer 23 (15%) to 44 (28%). The tables show its median concentration among cases where it was found did not rise; it fell in each disease (for example, lung cancer 14200 to 3920 fibers per gram).
  • Chrysotile was detected less often over time, in 13% to 15% of cases in group 1 versus 6% to 7% in group 2.
  • Median age at diagnosis rose in every disease group: mesothelioma 62 to 65 years (not significant), asbestosis 64 to 69 years, lung cancer 62 to 67 years.
  • Applying published attribution criteria, the authors classed 68 of 170 (40%) group 1 lung cancer cases and 34 of 170 (20%) group 2 lung cancer cases as asbestos related.
• The authors' conclusion: The authors concluded that the decrease in asbestos body and amosite concentrations over time is consistent with the 1972 banning of asbestos from insulation products. They found no source for the increased detection of crocidolite and said it needs further investigation.
• Limitations the authors state:
  • Most cases (about 60%) were medical-legal referrals and may not represent all asbestos-exposed people in the United States. The authors cite a prior comparison with the Australian Mesothelioma Registry suggesting little referral bias in exposure types, at least for mesothelioma.
  • Chrysotile breaks into thinner, shorter fibers and is cleared from the lungs more readily, so the method may underestimate it.
  • SEM is biased toward detecting commercial amphibole fibers such as amosite, while transmission electron microscopy is biased toward chrysotile.
  • Heavily loaded filters raised and varied the detection limit and could hide fiber types other than the main one. This happened in 44% of asbestosis cases, 14% of lung cancer cases and 9% of mesothelioma cases. The authors judged it an unlikely explanation for the chrysotile and crocidolite trends.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Carcinoma, Pleural Plaques, Malignant Mesothelioma, Mineral Fiber, Asbestos Body Formation, Scanning Electron Microscopy (SEM), Asbestos Bodies.

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