Asbestos-related mesothelioma: factors discriminating between pleural and peritoneal sites

Our plain-English summary of Asbestos-related mesothelioma: factors discriminating between pleural and peritoneal sites, by K. Browne, W.J. Smither (British Journal of Industrial Medicine, 1983).

The study

• Authors: K. Browne, W.J. Smither
• Journal: British Journal of Industrial Medicine
• Published: 1983;40(2):145-52
• Cited by: 71 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. 000598).

Abstract

Up to the end of 1980, 144 confirmed cases of mesothelioma were identified among employees of an organisation using asbestos in manufacturing and insulation. The primary site was peritoneal in 74 cases, pleural in 66, and undetermined in four. All employees had been exposed to amphibole asbestos, and evidence from different factories confirmed the predominant role of crocidolite in the production of mesothelioma. The ratio of pleural to peritoneal sites showed a continuous change when related to the year of first exposure, varying from 5:1 pleural to peritoneal before 1921 to 1:3 after 1950. The strong temporal relationship appeared to reflect progressive dust suppression, including the non-fibrous dusts present in insulation materials and perhaps also the degree to which the fibres had been opened. Other predisposing factors were related to the degree of individual exposure, the peritoneal site being associated preferentially with longer and heavier exposures.

In plain English

Authors from Cape Industries Ltd examined mesothelioma deaths among employees of their industrial group, which made asbestos products and did insulation (lagging) work. Cases required a postmortem, histology confirmed by the pneumoconiosis medical panel, and an adequate work history. Of 144 cases, 74 were peritoneal and 66 pleural, and in four the site of origin could not be determined. Peritoneal cases had been first exposed earlier on average (1936) than pleural cases (1942). Among workers first exposed before 1921 there was 1 pleural case to 5 peritoneal. Among those first exposed from 1951 there were 3 pleural to 1 peritoneal. At factory A, on a crude 1-to-6 job dust rating, peritoneal cases averaged 5.3 and pleural cases 4.8, a difference significant at the 5% level. Mean exposure was 138 months for peritoneal and 113 months for pleural cases, a difference that was not statistically significant. No mesothelioma was recorded at a factory using only chrysotile. The authors concluded that the differences were consistent with heavier exposure tending to produce peritoneal rather than pleural tumours. They found no good evidence that one fibre type favoured either site.

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: Case series: review of company and medical records of employees who died of mesothelioma, comparing pleural with peritoneal cases
• Who was studied: 144 confirmed mesothelioma cases among employees of a British industrial group (Cape Industries). Cases came from factory A in East London (1913-67), factory B in Yorkshire (1939-68), the lagging (insulation) division and other factories. All had a postmortem, histological confirmation by the pneumoconiosis medical panel, and an adequate work history. Factory A contributed 102 cases (64 men, 38 women).
• Exposure: Occupational exposure in asbestos manufacturing and insulation work. All employees had been exposed to amphibole asbestos. Factory A used crocidolite initially, with amosite and chrysotile from the late 1920s and early 1930s. Factory B used crocidolite, amosite and chrysotile. Factories C and D used mainly or only amosite, and factory E used only chrysotile. Severity of exposure at factory A was estimated with a 1-to-6 job rating scale, because no dust counts were available.
• Main results:
  • Of the 144 cases, 74 were peritoneal and 66 pleural; in 4, both pleura and peritoneum were affected and the site of origin could not be determined
  • At factory A, peritoneal cases exceeded pleural in a ratio of nearly 3:2. For laggers the two types were equal. At the remaining factories, where exposure was chiefly after 1945, pleural cases clearly outnumbered peritoneal.
  • The pleural-to-peritoneal ratio changed continuously and significantly with year of first exposure. In Table 6, the earliest group (first exposed before 1921) had 1 pleural and 5 peritoneal cases (ratio 0.2). The 1931-1940 group had 22 pleural and 29 peritoneal (ratio 0.76). Those first exposed from 1951 had 3 pleural and 1 peritoneal (ratio 3.0).
  • Mean year of first exposure was 1936 for peritoneal cases and 1942 for pleural cases (p = 0.001). Median years of death were 1969 and 1974 respectively.
  • On the factory A exposure rating scale, mesothelioma cases averaged 5.1. Peritoneal cases averaged 5.3 and pleural cases 4.8, a difference significant at the 5% level.
  • Mean exposure duration was 113 months for pleural cases and 138 months for peritoneal cases, a difference that was not statistically significant
  • Mean exposure duration for all cases was 10.5 years (range one month to 50 years). 32 cases (22%) were exposed for under one year, 21 (15%) for no more than six months, and nine (6%) for no more than three months.
  • Mean latent period (first known exposure to death) for the whole series was 32.3 years, with a standard deviation of nine and a range of 14 to 57 years. For women, the mean was 36.3 years. A longer latent period for peritoneal tumours appeared at all places of work.
  • Asbestosis: 36 cases (26%) had been certified with asbestosis while alive and 85 (60%) had asbestosis found at postmortem; it was absent in 20 (14%). Antemortem asbestosis was slightly more common with peritoneal (28%) than pleural (22%) cases, not statistically significant.
  • Factory C used amosite almost exclusively and employed roughly 6000 people from 1948; it had four mesothelioma deaths attributable to exposure there. No mesothelioma had been recorded at factory D (amosite only, average payroll 200) or at factory E (chrysotile only).
  • Histology reports were available for 50 cases. Excluding mixed types, 7 of 16 pleural cases (44%) were spindle cell type, compared with 3 of 15 peritoneal cases (20%) (p less than 0.05).
  • Among factory A employees whose main dust exposure was gas mask filter pad manufacturing, there were nine cases, eight of them peritoneal. Six of those eight had three years' exposure or less, and five had under one year.
  • A linear discriminant analysis using five variables correctly classified 63% of known cases as pleural or peritoneal (p = 0.01)
• The authors' conclusion: The authors concluded that the differences between pleural and peritoneal cases were small but consistent in direction. They said these differences fit the possibility that heavier exposure to asbestos dust tends to produce peritoneal rather than pleural mesotheliomas. They suggested other dusts, how far fibres had been opened, and fibre counts may play a part. They found no good evidence that one fibre type favoured either site.
• Limitations the authors state:
  • No dust counts were available, so severity of exposure was estimated with a crude job rating scale
  • Previous employment details were not recorded before 1939, so a very small number of cases may have had earlier, unrecorded exposure
  • Employees of factory B, and men employed since 1945, had not yet had time to contribute cases with long latencies, which affects the mean latency
  • Exposure at factories A and B could not be related to any single fibre type
  • The histological report was available for only 50 of the 144 cases

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Amphibole Asbestos, Crocidolite.

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