Malignant Mesothelioma In Quebec

Our plain-English summary of Malignant Mesothelioma In Quebec, by A.D. Mcdonald (1980).

The study

• Author: A.D. Mcdonald
• Published: Biological Effects Of Mineral Fibres (J.C. Wagner, Editor), Lyon: Iarc Scientific Publications, Volume 30, Pp. 673-680 (1980)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library, J-M no. 002181. The article is still under copyright, so we describe it here rather than post it.

In plain English

This paper reviewed all 254 fatal mesothelioma cases known to the author's group in Quebec from 1960 to 1978. Cases came from three overlapping sources: a cohort of chrysotile miners and millers, pathologists' reports, and follow-up of workers making crocidolite gas-mask filter pads in 1939-1941. Of the 254 cases, 181 were men and 73 women. About 40% of the male cases were judged probably attributable to occupational asbestos exposure. Four of the 63 women traced had worked with asbestos. Within 50 years of first employment, 22 cases occurred among workers of three factories. Only 10 occurred among chrysotile miners and millers, a workforce more than eight times larger. Sixteen of 25 factory-worker cases had worked with asbestos under five years, against 2 of 16 miners and millers. All tumours in miners and millers were pleural; one, in a man probably exposed to crocidolite, also affected the peritoneum. The author concluded that the evidence supports the view that mesothelioma risk after crocidolite is many times greater than after chrysotile. The author noted that case-finding was probably incomplete in some years.

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: Review of all known fatal mesothelioma cases in a province (case series drawn from three overlapping sources), with controls investigated for 1960-1972 only
• Who was studied: 254 fatal mesothelioma cases in the Province of Quebec, 1960-1978 (181 males, 73 females); occupational and residential histories were obtained for 165 males and 63 females
• Exposure: Chrysotile mining and milling; crocidolite used to make military gas-mask filter pads (1939-1941); factory manufacture using chrysotile, amosite and crocidolite; also insulation, heating trades, shipyards, construction, and household exposure
• Main results:
  • 21 of the 254 cases had worked in the chrysotile mining industry. Five of these had also been exposed to crocidolite in gas-mask filter manufacture at Factory A, leaving 16 who had worked in the mines and mills only. Two of the 16 may also have been exposed to crocidolite in one mill.
  • Among male cases for 1960-1972, 18 (20.5%) had worked in asbestos production, asbestos manufacture or insulation, compared with one control (1.2%; one of 81 controls traced in Table 1).
  • Heating trades, shipyards and construction were also reported for 17.3% of controls for 1960-1972.
  • Over the whole period, about 40% of male cases were judged probably attributable to occupational asbestos exposure.
  • The estimated average number of men dying each year from mesothelioma due to asbestos exposure was 3.5 in 1965-1968, rising to about 10 in 1977-1978. On average, 4.6 male cases a year from 1965 through 1978 were not associated with asbestos exposure.
  • Among the 63 women traced, four (printed as 5.4%) had been exposed occupationally to asbestos, all in factories. Four others were daughters of chrysotile miners or millers, and one was the wife of an insulator.
  • The four daughters of chrysotile miners or millers were thought probably to have been exposed through their fathers' dusty clothing.
  • The average annual number of cases in unexposed females was 3.2, fairly similar to 4.6 for unexposed males.
  • 22 cases occurred within 50 years of first employment in Factories A (5), B (9) and C (8). No cases were found in employees of Factory D, which used only chrysotile.
  • Among chrysotile miners and millers, a workforce more than eight times larger, there were only 10 cases within the same interval, or eight if the two probably also exposed to crocidolite were excluded.
  • The median interval from first employment to death was 44 years for chrysotile miners, compared with 29 years for factory workers.
  • 16 of the 25 factory-worker cases had worked with asbestos for less than five years, compared with two of the 16 miners and millers.
  • All tumours in miners and millers were pleural, except one that affected both pleura and peritoneum, in a man probably exposed to crocidolite.
  • Among factory workers, eight tumours (32%) were peritoneal and two (8%) were pleural and peritoneal.
• The authors' conclusion: The author concluded that the evidence from this survey supports the view that the risk of mesothelioma after exposure to crocidolite is many times greater than after chrysotile. The author also concluded that, once cases attributable to occupational asbestos exposure were excluded, incidence was similar in men and women, and that these remaining cases may possibly have some other cause.
• Limitations the authors state:
  • Case-finding was likely more complete in the cohort studies than in the inquiry through pathologists.
  • The low case numbers in 1960-1964 and 1977-1978 were probably due to incomplete case-finding.
  • The number of persons exposed in various ways since the beginning of the century could not be estimated.
  • Workforce sizes in 1977 were assumed to reflect the relative numbers employed in the past.
  • Controls were not investigated for 1973-1978.
  • No direct measurements of dust exposure were available for the processes where crocidolite was used.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chrysotile, Crocidolite, Filter pad, Asbestos Exposure, Peritoneum.

Browse return to medical research.