The Association between the Histological Subtypes of Mesothelioma and Asbestos Exposure Characteristics

Our plain-English summary of The Association between the Histological Subtypes of Mesothelioma and Asbestos Exposure Characteristics, by T. Vorster, J. Mthombeni, J. teWaterNaude, et al (International Journal of Environmental Research and Public Health, 2022).

The study

• Authors: T. Vorster, J. Mthombeni, J. teWaterNaude, J.I. Phillips
• Journal: International Journal of Environmental Research and Public Health
• Published: 2022;19(21)
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos mining operations have left South Africa with a legacy of asbestos contamination and asbestos-related diseases continue to be a problem. The large-scale mining of three types of asbestos presents a unique opportunity to study malignant mesothelioma of the pleura (mesothelioma) in South Africa. This study aimed to describe the demographics of deceased individuals diagnosed with mesothelioma and explore any associations between the histological morphology of mesothelioma and asbestos characteristics. We reviewed the records of all deceased miners and ex-miners from the Pathology Automation System (PATHAUT) database of the National Institute of Occupational Health (NIOH) that were histologically diagnosed with mesothelioma in the period from January 2006-December 2016 (11 years). The study population does not include all cases of mesothelioma in South Africa but rather those that reached the compensation system. Crocidolite asbestos fibres were identified in the majority of mesothelioma cases (n = 140; 53.4%). The epithelioid subtype was most commonly present in both occupational and environmental cases. Cases with the sarcomatous subtype were older at death and fewer female cases were diagnosed with this subtype. No relationship between mesothelioma subtype and asbestos type or asbestos burden or fibre size was established.

In plain English

This cross-sectional study reviewed the records of 270 deceased miners and ex-miners in South Africa who were diagnosed at autopsy with malignant mesothelioma of the pleura between January 2006 and December 2016. The records came from the National Institute of Occupational Health's PATHAUT database, so only cases that reached the compensation system were included. Of the 270, 89.3% were occupationally exposed and 10.7% environmentally exposed. Lung fibre analysis was done for 262 cases. Crocidolite alone was found in 140 (53.4%) and no asbestos fibres in 98 (37.4%). One case contained chrysotile, together with amosite. The epithelioid subtype was the most common (174 of 270, 64.4%) in both exposure groups. Sarcomatous cases had a higher mean age (68.8 years) than biphasic (62.8) or epithelioid (63.6) cases, a statistically significant difference. Three of 33 sarcomatous cases (9.1%) were female, against 20.6% of biphasic and 19.0% of epithelioid cases, but the subtype pattern did not differ significantly between women and men. No statistically significant relationship was found between subtype and asbestos type, fibre size or fibre burden.

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: Cross-sectional study of existing autopsy pathology records and lung fibre analysis records
• Who was studied: 270 deceased miners and ex-miners in South Africa, histologically diagnosed with mesothelioma (malignant mesothelioma of the pleura) at autopsy and recorded in the PATHAUT database of the National Institute of Occupational Health, January 2006 to December 2016. Only cases that reached the compensation system were included. 214 (79.3%) were male, and the mean age was 64.0 years (standard deviation 10.8).
• Exposure: Cases were classed as occupationally exposed (89.3%) or environmentally exposed (10.7%). Occupational cases had often worked in several kinds of mines; their exposure was assigned by longest service, which was in asbestos mining for 112 (46.5%). Lung fibre burden was measured by electron microscopy for asbestos type (crocidolite, amosite, chrysotile), fibre size (1 to 5, over 5 to 10, and over 10 micrometres) and concentration per gram of dry lung.
• Main results:
  • Of the 262 cases sent for fibre analysis, crocidolite alone was found in the lungs of 140 (53.4%), and no asbestos fibres were identified in 98 (37.4%).
  • Only one case contained chrysotile fibres, and these were found together with amosite fibres. No case had chrysotile alone.
  • The epithelioid subtype made up 174 of 270 cases (64.4%), biphasic 63 of 270 (23.3%) and sarcomatous 33 (12.2%).
  • The pattern of subtypes did not differ significantly between environmentally exposed cases (69.0% epithelioid) and occupationally exposed cases (63.9% epithelioid), p = 0.65.
  • Mean age differed across subtypes (analysis of variance p = 0.02). Sarcomatous cases had the highest mean age, 68.8 years (standard deviation 9.4), and biphasic cases the lowest, 62.8 years (standard deviation 9.9).
  • In pairwise comparisons, mean age differed between sarcomatous and biphasic cases (68.8 vs 62.8 years, p = 0.03).
  • Mean age also differed between sarcomatous and epithelioid cases (68.8 vs 63.6 years, p = 0.03). Biphasic and epithelioid cases did not differ (p = 1.00).
  • Three of the sarcomatous cases (9.1%) were female, compared with 20.6% of biphasic and 19.0% of epithelioid cases.
  • The pattern of subtypes was not significantly different between females and males (p = 0.65).
  • Mean concentrations of asbestos bodies and fibres were generally higher in the lungs of occupationally exposed cases than environmentally exposed cases.
  • Among the 164 cases with both a subtype and an asbestos type identified, there was no statistically significant relationship between asbestos type and subtype (p = 0.51). Crocidolite was found in 85.3% of epithelioid, 88.9% of biphasic and 78.9% of sarcomatous cases.
  • There were no statistically significant differences in asbestos fibre sizes across subtypes. For fibre size and number ranges, the p-values were 0.64, 0.46 and 0.84 for the three crocidolite size groups and 0.68, 0.75 and 0.34 for the three amosite size groups.
• The authors' conclusion: The authors concluded that no strong evidence was found for any relationship between mesothelioma subtype and asbestos type, fibre size or asbestos burden. They noted a statistically significant age difference between sarcomatous and the other two subtypes, and said further research on the subtypes is necessary.
• Limitations the authors state:
  • The study population does not include all mesothelioma cases in South Africa, only those that reached the compensation system.
  • Citing another study, the authors state that PATHAUT cases equal about 18% of all reported mesothelioma cases in South Africa.
  • Occupational cases often had mixed exposures from working in different mines, but exposure was assigned by longest service history.
  • Women were never formally employed in asbestos mines. This may explain why few women were identified, especially among occupational cases, and some may have been counted as environmental cases.

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: Histological Subtype, Mesothelioma, Asbestos Exposure, Malignant Mesothelioma, Pleura, Pathology, Crocidolite, Epithelioid.

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