Malignant mesothelioma: incidence, asbestos exposure, and reclassification of histopathology

Our plain-English summary of Malignant mesothelioma: incidence, asbestos exposure, and reclassification of histopathology, by W.E. Wright, R.P. Sherwin, E.A. Dickson, et al (British Journal of Industrial Medicine, 1984).

The study

• Authors: W.E. Wright, R.P. Sherwin, E.A. Dickson, L. Bernstein, J.B. Fromm, B.E. Henderson
• Journal: British Journal of Industrial Medicine
• Published: 1984;41(1):39-45
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000652).

Abstract

The Los Angeles County Cancer Surveillance Program abstracts records on almost all cases of cancer occurring in the county. In a study of those cases of pleural and peritoneal malignant mesothelioma (MM) that occurred from 1972 to 1979 occupational histories were obtained during interviews, and histopathology of the tumours was reviewed and classified by a member of a mesothelioma reference panel who was unaware of the exposure histories. About half the cases reviewed had likely exposure to asbestos at work. The greatest proportion of cases designated as MM by the pathologist occurred among individuals likely to have had the heaviest exposure of asbestos (42%). No upward trend of incidence over time was apparent among cases designated as MM. The age adjusted incidence rates for designated MM were lower than in other studies. The well recognised interobserver variability in diagnosing MM apparently produces raised estimates of incidence and an overestimate of trends of incidence. The interobserver variability may result from different awareness of MM occurrence, a lack of precise histopathological criteria for the diagnosis, or the influence of a history of exposure to asbestos on the interpretation. A history of exposure to asbestos may bias interpretation of histopathology and should not be used to make the histological diagnosis.

In plain English

The authors used the Los Angeles County cancer registry to collect 212 cases recorded as pleural or peritoneal mesothelioma diagnosed from 1972 to 1979. A reference-panel pathologist, given no clinical or exposure information, re-examined tissue from 162 cases. The pathologist judged 42 (26%) to be definite, probable, or possible mesothelioma, while 46 men and 8 women were judged to have cancers arising outside the pleura or peritoneum. Work histories came from interviews, mostly with relatives. Of 134 cases with both slides and histories, 71 (53%) had probably been exposed to asbestos at work, but only 20 of those 71 (28%) were designated mesothelioma. Among men, the share designated mesothelioma was highest in asbestos production and manufacture (4/9) and shipyards (8/20), and lowest in construction (1/12). Age-adjusted incidence for all collected cases was 7.0 per million person-years in men and 1.8 in women. After reclassification the estimates were 1.95 and 0.36, and no continuing upward trend was seen. The authors concluded that incidence estimates without pathology verification may substantially overestimate incidence. They noted that the review reflected one pathologist's view.

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: Population-based registry case series: cases reported as mesothelioma were re-reviewed by a pathologist blinded to exposure, and the reclassified diagnoses were related to occupational asbestos exposure (from interviews) and to incidence
• Who was studied: 212 cases recorded as pleural (182) or peritoneal (30) mesothelioma, first diagnosed in Los Angeles County, USA, from 1972 to 1979. 161 cases were male. About 60% of 1979 cases were available. Tissue was adequate for review in 162 cases (122 men, 40 women). 134 cases had both adequate slides and interview histories.
• Exposure: Occupational asbestos exposure, judged from job histories by an author who did not know the pathology. Jobs counted as likely exposure were insulation, asbestos production and manufacture, heating trades, shipyards and the construction industry. A yes or no question about work with asbestos was also asked. Fiber types were not specified.
• Main results:
  • Of 162 cases with adequate tissue, the review pathologist designated 42 (26%) as definite, probable, or possible mesothelioma (34 men, 8 women).
  • 46 men (38%) and 8 women (20%) were judged to have tumours from a primary site other than the pleura or peritoneum.
  • Of 134 cases with adequate slides and histories, 71 (53%) had probably been exposed to asbestos at work. The figure was 69/103 (67%) for men and 2/31 (7%) for women.
  • The proportion exposed was 20/34 (59%) among cases designated mesothelioma and 28/52 (54%) among cases judged definitely to be other cancers.
  • Of all subjects exposed to asbestos at work, 20/71 (28%) were designated definite, probable, or possible mesothelioma.
  • Among 103 men, the proportion of cases designated mesothelioma was 4/9 (44%) in asbestos production and manufacture and 8/20 (40%) in shipyard work. All the shipyard workers' designated mesotheliomas were pleural.
  • Among men, insulation work had 2/8 (25%) designated mesothelioma, heating trades 4/20 (20%), and the construction industry 1/12 (8%).
  • For designated mesothelioma cases, the average period from first likely asbestos exposure to diagnosis was 37.9 years (range 26 to 54).
  • Age-adjusted incidence for all 212 collected cases was 7.0 per million person-years for men and 1.8 for women. After adjusting by the proportion of designated cases, the estimates were 1.95 per million person-years for men and 0.36 for women.
  • Before reclassification there was a distinct upward trend in incidence, peaking in 1976. For designated cases, rates rose in 1975 to 1976 and then fell back to pre-1975 levels, with no continuing upward trend.
• The authors' conclusion: The authors concluded that mesothelioma incidence estimates from cancer registries or other records without histopathological verification may substantially overestimate incidence.
• Limitations the authors state:
  • The reclassification reflects a single pathologist's view. Given interobserver variability, another pathologist or a panel would accept a different number of cases, so the study is not a definitive count of mesotheliomas.
  • Occupational histories from family members often lacked the detail needed to identify exposure in other possibly exposed jobs (e.g. garage work, building maintenance, sheet metal work), so those exposures were underestimated.
  • Other occupational, take-home, hobby-related and environmental asbestos exposures could not be accurately assessed.
  • Because of reporting delays, only about 60% of 1979 cases were available.

Topics

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

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Asbestos Exposure, Histopathology, Mesothelioma, Incidence.

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• Incidence and survival of peritoneal malignant mesothelioma between 1989 and 2015: A population-based study — N. Le Stang, V. Bouvier, et al. (2019)
• Histopathology of removed indwelling pleural catheters from patients with malignant pleural diseases — C.L. Tobin, R. Thomas, et al. (2016)
• Time trend of mesothelioma incidence in the United States and projection of future cases: an update based on SEER data for 1973 through 2005 — B. Price, A. Ware (2009)
• The incidence of malignant mesothelioma in Australia, 1947-1980 — A.W. Musk, P.J. Dolin, et al. (1989)

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