Asbestos exposure and histological subtype of malignant mesothelioma

Our plain-English summary of Asbestos exposure and histological subtype of malignant mesothelioma, by P. Franklin, H. Alfonso, A. Reid, et al (Occupational and Environmental Medicine, 2016).

The study

• Authors: P. Franklin, H. Alfonso, A. Reid, N. Olsen, K.B. Shilkin, F. Brims, N. de Klerk, A.W. Musk
• Journal: Occupational and Environmental Medicine
• Published: 2016;73(11):749-752
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Malignant mesothelioma (MM) has distinct histological subtypes (epithelioid, sarcomatoid and biphasic) with variable behaviour and prognoses. It is well recognised that survival time varies with the histological subtype of MM. It is not known, however, if asbestos exposure characteristics (type of asbestos, degree of exposure) are associated with different histological subtypes.

Aim: To determine if the pathological MM subtype is associated with the type of asbestos or the attributes of asbestos exposure.

Methods: Cases of MM for the period 1962 until 2012, their main histological subtype and their most significant source of asbestos exposure were collected from the Western Australian Mesothelioma Registry. Exposure characteristics included, degree of asbestos exposure (including total days exposed, years since first exposure and, for crocidolite only, calculated cumulative exposure), source of exposure (occupational or environmental), form of asbestos handled (raw or processed) and type of asbestos (crocidolite only or mixed fibres).

Results: Patients with the biphasic subtype were more likely to have occupational exposure (OR 1.83, 1.12 to 2.85) and exposure to raw fibres (OR 1.58, 1.19 to 2.10). However, differences between subtypes in the proportions with these different exposure characteristics were small and unlikely to be biologically relevant. Other indicators of asbestos exposure were not associated with the histological subtype of mesothelioma.

Conclusions: There was no strong evidence of a consistent role of asbestos exposure indicators in determining the histological subtype of MM.

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In plain English

This study used the Western Australian Mesothelioma Register to ask whether asbestos exposure features were linked to the microscopic subtype of malignant mesothelioma (epithelioid, biphasic or sarcomatoid). The register held 2024 confirmed cases from 1960 to December 2012; 1656 were analysed. Where information was available, each case's main exposure was classed as occupational or non-occupational; raw, processed or unclear asbestos; and crocidolite only (Wittenoom mine, mill or town) or mixed fibres. Compared with epithelioid cases, biphasic cases more often had occupational exposure (333 of 380, 87.6%, versus 496 of 614, 80.8%) and raw asbestos exposure (47.8% versus 36.9%, among cases with data on asbestos form). No significant difference was found for crocidolite-only exposure. Among 341 Wittenoom cases, biphasic cases had a significantly shorter duration of exposure, but cumulative exposure did not differ. In 122 lung tissue samples, fibre numbers and proportions did not differ across subtypes. The authors called these differences small. They concluded that the findings did not show a consistent role for asbestos exposure in determining subtype. They noted possible misclassification of subtype and incomplete exposure information.

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: Analysis of cases from a population-wide mesothelioma register, comparing exposure characteristics across histological subtypes using regression models adjusted for age and sex
• Who was studied: All confirmed malignant mesothelioma cases on the Western Australian Mesothelioma Register, 1960 to December 2012: 2024 cases (1744 males). After excluding 140 cases with undetermined subtype and 228 with unknown or no-known exposure, 1656 cases were analysed: 614 epithelioid, 440 cytology only, 380 biphasic and 222 sarcomatoid.
• Exposure: Where information was available, each case's most significant asbestos exposure was classed by three features. Source was occupational or non-occupational. Form was raw (mining, transport, asbestos production, or Wittenoom residence or visits), processed (asbestos products), or unclear. Type was crocidolite only (Wittenoom workers and residents) or mixed fibres. Duration of exposure (occupational cases only) and time since first exposure were also assessed, and cumulative exposure for Wittenoom cases only. Lung asbestos bodies and fibres were counted in a subsample of 122 cases.
• Main results:
  • Occupational exposure was found in 333 of 380 biphasic cases (87.6%) and 496 of 614 epithelioid cases (80.8%). The age- and sex-adjusted OR for biphasic compared with epithelioid was 1.83 (95% CI 1.18 to 2.85).
  • Raw asbestos exposure was found in 155 biphasic cases (47.8%) and 197 epithelioid cases (36.9%). These numbers are lower because of missing data, so the percentages are of cases with information on asbestos form. The adjusted OR for biphasic compared with epithelioid was 1.58 (95% CI 1.19 to 2.10). For cytology-only compared with epithelioid cases, the OR for raw fibre was 1.38 (1.05 to 1.82).
  • Crocidolite-only (Wittenoom) exposure did not differ significantly between the groups. The adjusted OR for biphasic compared with epithelioid was 1.28 (0.97 to 1.70), and for sarcomatoid compared with epithelioid 0.78 (0.54 to 1.14).
  • Among 341 Wittenoom cases, cumulative exposure and average daily exposure intensity did not differ between subtypes. Biphasic cases had a significantly shorter duration of exposure (geometric mean 367.2 days exposed) than epithelioid cases (559.5 days).
  • In 122 lung tissue samples, crocidolite was found in 98.3% of samples, chrysotile in 31.9% and amosite in 13.1%. Fibre numbers and proportions did not differ across the histological groups.
• The authors' conclusion: The authors concluded that some differences in exposure characteristics were found between subtypes, but they were small. In the authors' view, these differences did not provide evidence for a consistent role of asbestos exposure indicators in determining the histological subtype of malignant mesothelioma.
• Limitations the authors state:
  • Subtype classification may be wrong in individual cases, particularly for the biphasic subtype.
  • Cases diagnosed by cytology only were recorded as epithelioid, but some may have been biphasic, so they were analysed as a separate group.
  • Exposure was assessed from occupational histories, self-reported questionnaires and clinical notes. The single primary route of exposure assigned to each case is unlikely to reflect all routes and types of exposure.
  • The effects of individual fibre types were hard to separate, because the mixed-fibre group probably also had some crocidolite exposure.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Histological Subtype, Malignant Mesothelioma, Epithelioid, Sarcomatoid, Biphasic Mesothelioma, Mesothelioma, Crocidolite.

Related studies

• Incidence of malignant mesothelioma in Aboriginal people in Western Australia — P. Franklin, A. Reid, et al. (2016)
• The Association between the Histological Subtypes of Mesothelioma and Asbestos Exposure Characteristics — T. Vorster, J. Mthombeni, et al. (2022)
• The Wittenoom legacy — A.W.B. Musk, A. Reid, et al. (2020)
• Autoimmune antibodies and asbestos exposure: Evidence from Wittenoom, Western Australia — A. Reid, P. Franklin, et al. (2018)
• Predicting survival in malignant mesothelioma — A.W. Musk, N. Olsen, et al. (2011)
• Risk factors for malignant mesothelioma in people with no known exposure to asbestos — B. Musk, L. Gordon, et al. (2017)

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