Epidemiologic surveillance of mesothelioma in Canada

Our plain-English summary of Epidemiologic surveillance of mesothelioma in Canada, by A.D. McDonald, J.C. McDonald (Canadian Medical Association Journal, 1973).

The study

• Authors: A.D. McDonald, J.C. McDonald
• Journal: Canadian Medical Association Journal
• Published: 1973;109(5):359-62
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 002399).

Abstract

The number of fatal malignant mesotheliomas was ascertained for the period 1960-70 by contacting all pathologists in Canada. The annual incidence was steady between 1966 and 1970 at 1.4 per million population. Of 71 cases registered in 1968-70 and not previously reported, 66% were pleural, 24% peritoneal and the remainder in both sites; 45% of tumours were in women. The diagnosis of mesothelioma was approved by the Canadian Mesothelioma Panel in 59%. Sixty-nine cases were successfully investigated epidemiologically. A history of definite or probable occupational asbestos exposure was found in 30% of male cases compared with 11% of controls, but in none of the female cases or controls. However, among cases, four women and one man had had domestic exposure to dusty clothing of an asbestos worker. Most of the excess occupational exposure was in the manufacture of asbestos products or insulation and little in mining or milling. No case other than those occupationally or domestically exposed had lived within 20 miles of asbestos mines or mills.

In plain English

Continuing a national survey, the authors asked all 453 Canadian pathologists about fatal malignant mesothelioma and recorded 71 deaths from July 1968 through 1970. Of these, 47 (66%) were pleural, 17 (24%) peritoneal and 7 (10%) both; 32 (45%) were women. Each case had a matched control who died with lung metastases from a cancer elsewhere. A pathology panel favoured the diagnosis in 42 (59%). Mean annual incidence since 1966 was 1.4 per million population. Definite or probable direct or indirect occupational asbestos exposure was reported in 29.7% of male cases and 10.5% of male controls. Among women, none had definite or probable occupational exposure; it was possible in 12.5% of cases and 9.4% of controls. Four female cases and one female control had home exposure to an asbestos worker's dusty clothing. Manufacture of asbestos products or insulation work was recorded in nine cases and no controls. The authors concluded asbestos exposure was associated with a relatively small proportion of these tumours. They also saw no indication of changing incidence, though the survey would need extending to confirm this.

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-control study within a national surveillance survey of fatal mesothelioma cases reported by pathologists. Each case was matched to a control. Relatives were interviewed without the interviewers knowing which was a case.
• Who was studied: 71 fatal cases of mesothelioma in Canada, with death from July 1968 to the end of 1970, found by contacting 453 pathologists. Controls were 71 patients with lung metastases from tumours outside the chest. They were matched for sex and as closely as possible for age and date of death. 69 cases were successfully investigated.
• Exposure: Occupational asbestos exposure, classed as definite, probable or possible, and domestic exposure to the dusty clothing of asbestos workers. The study also looked at residence near asbestos mines or mills, other workplace materials (cement, copper, fibreglass, nickel, rubber, wood) and cigarette smoking. No fiber type was specified.
• Main results:
  • Among the 71 cases, 47 (66%) were pleural tumours, 17 (24%) peritoneal and 7 (10%) both. 39 (55%) were in men and 32 (45%) in women.
  • The Mesothelioma Panel was in favour of the diagnosis in 42 cases (59%), uncertain in 5 (7%) and against it in 24 (34%).
  • The mean annual incidence of mesothelioma in Canada since 1966 was 1.4 per million population, and the annual number of cases fluctuated little.
  • Eleven men with mesothelioma had worked with asbestos, compared with four male controls. Among these 11 cases, exposure was definite in seven and probable in four. Exposure was probable in all four controls.
  • Probable or definite direct or indirect occupational exposure was reported in 29.7% of male cases and 10.5% of male controls.
  • No woman had definite or probable occupational exposure. Possible occupational exposure was reported in 12.5% of female cases and 9.4% of female controls.
  • None of the 32 female cases had definite or probable occupational asbestos exposure. Four had been exposed at home to dusty clothing brought home by a father (two) or a husband (two) who worked with asbestos. Only one female control had such exposure.
  • Manufacture of asbestos products or insulation work was recorded in nine cases and no controls. Mining or milling was recorded in three cases and no controls. Other occupations were recorded in four cases and five controls.
  • Apart from people who were themselves occupationally or domestically exposed, no case had lived within 20 miles of asbestos mines or mills.
  • Three men had worked with asbestos for one year or less; their intervals from exposure to death were 26, 26 and 33 years. One man who died at 91 had worked in asbestos mines between ages 15 and 24. For the remaining seven exposed men, the interval between first exposure and death was 19 to 61 years.
  • Smoking histories of male cases closely resembled those of male controls. Women with mesothelioma were less often non-smokers than female controls: 14 (45.2%) of 31 cases versus 22 (68.8%) of 32 controls.
  • Across 1960-70, 13 (42%) of 31 asbestos-exposed male cases smoked more than 10 cigarettes daily, compared with 52 (40%) of 132 controls. The authors found no evidence that smoking potentiates asbestos exposure in producing mesothelioma.
• The authors' conclusion: The authors concluded that asbestos exposure is associated with a relatively small proportion of the tumours Canadian pathologists call mesotheliomas. They found that the steady annual number of cases since 1966 gave no indication of a change in incidence. They also found that the main findings were very similar to those of the earlier 1960-67 period.
• Limitations the authors state:
  • Numbers were small, so the larger proportion of female cases and the higher panel approval in women may have been due to chance.
  • The survey would need to be extended for at least several more years to confirm that incidence is not changing.
  • The higher incidence in Quebec may not be real, because the panel accepted the diagnosis in a much lower proportion of Quebec cases.
  • Exposure was reported more often than in the earlier series. This may partly reflect the shorter time between death and interview of relatives. A higher proportion of male subjects also came from urban industrialized areas.

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: Mesothelioma, Malignant Mesothelioma, Asbestos Exposure, Occupational Exposure.

Related studies

• Epidemiology of primary malignant mesothelial tumors in Canada — A.D. McDonald, A. Harper, et al. (1970)
• Surveillance of mesothelioma and workers' compensation in British Columbia, Canada — T.L. Kirkham, M.W. Koehoorn, et al. (2011)
• Mortality experience of insulation workers in the United States and Canada, 1943--1976 — I.J. Selikoff, E.C. Hammond, et al. (1979)
• Critical review of epidemiologic studies related to ingested asbestos — G.M. Marsh (1983)
• Respiratory carcinogenesis: an epidemiologic appraisal — J.F. Fraumeni (1975)
• Environmental fiber-induced pleuro-pulmonary diseases in an Anatolian village: an epidemiologic study — M. Artvinli, Y.I. Baris (1982)

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