Malignant mesothelioma in North America

Our plain-English summary of Malignant mesothelioma in North America, by A.D. McDonald, J.C. McDonald (Cancer, 1980).

The study

• Authors: A.D. McDonald, J.C. McDonald
• Journal: Cancer
• Published: 1980;46(7):1650-6
• Cited by: 230 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 002042).

Abstract

Ascertainment, through 7,400 pathologists, of all fatal malignant mesothelial tumors in Canada (1960-75) and the U.S.A. (1972) gave a total of 668 cases (272 in 1972). In Canada, the annual number of male cases rose from about 17 in 1966 to 25 in 1972 but the number of female cases remained fairly steady at a much lower level. The annual incidence in North America in 1972 was estimated at 2.8 per million males and 0.7 per million females aged 15 years and over. Occupational histories were obtained "blind" for 480 of the 557 cases through 1972, and their matched controls; relative risks were as follows: insulation work, 46.0 asbestos production and manufacture, 6.1, heating trades (other than insulation) 4.4. For nearly half the male cases and for about 5% of female cases, the tumor could be attributed to occupational exposure to asbestos, of which a fifth were in shipyards. No indication was found of other possible causes (including man-made mineral fibers, tobacco smoking, or residence near zeolite deposits). Four subjects were men who had been employed in Quebec chrysotile mines and 3 were children of employees, but no other subject had lived in the mining area. The findings remain consistent with a much greater mesothelioma-producing potential for crocidolite and amosite than for chrysotile; however, further studies of factory workers exposed to chrysotile only are needed to confirm this. Mineral fiber analysis of lung tissue from patients and controls is in progress.

In plain English

The authors combined their pathologist-based surveys of fatal malignant mesothelioma in Canada (1960-75) and the U.S.A. (1972): 668 cases. Relatives of cases and matched controls dying of other cancers described jobs, homes and smoking. The estimated 1972 rate was 2.8 per million men and 0.7 per million women aged 15 and over. In 344 male pairs, men counted once, in their highest-ranked job group; each group was compared with men in other listed asbestos-related jobs and unlisted jobs combined. Relative risks were 46.0 for insulation, 6.1 for asbestos production and manufacture, 4.4 for other heating trades; excluding insulation and heating work, 2.8 for shipyards and 2.6 for construction. The authors attributed nearly half of male and about 5% of female cases to occupational asbestos exposure. Eight cases, versus two controls, had been exposed at home to asbestos workers' dusty clothing. The authors concluded the findings remained consistent with much greater mesothelioma-producing potential for crocidolite and amosite than chrysotile, needing confirmation in chrysotile-only factory workers. They estimated about 30% of cases were missed, roughly balanced by a similar proportion rejected by pathology panels.

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: Matched case-control study built on attempted complete national ascertainment of fatal cases through pathologists. The report brings together several of the authors' published and unpublished surveys.
• Who was studied: Fatal malignant mesothelial tumors reported by pathologists in Canada (1960-75) and the U.S.A. (1972): 668 cases in total. Of the 557 cases through 1972, 395 were male and 162 female. Controls were matched for sex, age and year of death and had died with lung metastases from a non-lung cancer. Occupational analyses used 344 male case-control pairs (185 Canadian, 159 U.S.).
• Exposure: Occupations were grouped as insulation, asbestos production and manufacture, heating trades, shipyards, construction, other listed asbestos jobs, and unlisted jobs. The study also examined household exposure to dusty work clothing, living within 20 miles of an asbestos mine or (in the U.S.A.) a zeolite deposit, dust from fiberglass, cement, rubber, copper, nickel and wood, and cigarette smoking.
• Main results:
  • The estimated annual incidence in North America in 1972 was 2.8 per million males and 0.7 per million females aged 15 years and over.
  • In Canada, the annual number of male cases rose from about 17 in 1966 to 25 in 1972. Female cases stayed fairly steady at a much lower level.
  • Among male cases, 307 (78%) were pleural (including three pericardial tumors) and 88 (22%) were peritoneal.
  • For the occupational relative risks, the five job groups were made mutually exclusive: each man was entered once, in the highest-ranked group he qualified for. Each group was compared with men in group F (other listed jobs thought to entail asbestos exposure) and group G (unlisted jobs) taken together.
  • On this basis, for male case-control pairs in both countries combined, relative risks were 46.0 for insulation, 6.1 for asbestos production and manufacture, and 4.4 for heating trades other than insulation.
  • After excluding men who had worked in insulation or heating trades, relative risks were 2.8 for shipyard work and 2.6 for construction.
  • The authors attributed the tumor to occupational asbestos exposure for nearly half of male cases and about 5% of female cases. A fifth of these were in shipyards.
  • Two male and 6 female cases, but none of their matched controls, had been exposed at home to an asbestos worker's dusty clothing. Two controls had such exposure when their paired cases did not; the paired comparison gave P = 0.08.
  • Among male pairs, only fiberglass dust showed an increased relative risk. After allowing for asbestos exposure, it fell to 1.62 (95% confidence limits 0.75 and 3.53).
  • Living within 20 miles of reported zeolite deposits in the western U.S.A. gave a paired relative risk of 1.83. This fell to 1.60 after allowing for occupational asbestos exposure; the article prints the limits as 75% confidence limits, 0.58 and 4.93.
  • No association between cigarette smoking and mesothelioma was found for male cases.
  • The authors found no indication of other possible causes, including man-made mineral fibers, tobacco smoking, or residence near zeolite deposits.
  • Four cases were men who had worked in Quebec chrysotile mines and 3 were children of employees. No other case had lived in the mining area.
• The authors' conclusion: The authors concluded that the findings remain consistent with a much greater mesothelioma-producing potential for crocidolite and amosite than for chrysotile. They said further studies of factory workers exposed to chrysotile only are needed to confirm this.
• Limitations the authors state:
  • The authors estimated that the survey probably underestimated true incidence by about 30%. They added that this was balanced by an almost similar proportion of cases rejected by the pathology panels.
  • Case finding was probably incomplete before ascertainment began in 1967, which may explain part of the early rise in Canadian cases.
  • Exposure histories came from questioning relatives after death. The authors noted that the proportion of cases attributable to asbestos may therefore be somewhat underestimated.

Topics

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

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Relative Risk, Occupational Exposure, Mineral Fiber, Zeolite, Quebec Chrysotile, Mesothelioma, Crocidolite.

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