Cancer in asbestos-mining and other areas of Quebec

Our plain-English summary of Cancer in asbestos-mining and other areas of Quebec, by S. Graham, M. Blanchet, T. Rohrer (Journal of the National Cancer Institute, 1977).

The study

• Authors: S. Graham, M. Blanchet, T. Rohrer
• Journal: Journal of the National Cancer Institute
• Published: 1977;59(4):1139-45
• Cited by: 22 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. 002234).

Abstract

Employing incidence data from the Quebec Tumor Registry, we examined the relative risks of cancer of all sites for the years 1969-73 in the asbestos-mining, rural, and metropolitan counties of Quebec Province, Canada. Generally, rates for males exceeded those for females, and the relative risks in the asbestos-mining counties for 7-10 different sites of cancer, all of low incidence, were from 1.50 to 8.08 times those of other rural counties of the Province for both sexes. Metropolitan counties exhibited equally high risk for many of these sites. We discovered higher risks among males in asbestos-mining counties for cancer of the pleura, peritoneum, lip, tongue, salivary gland, mouth, and small intestine and higher risks among females for cancer of the pleura, lip, kidney, salivary gland, and for melanoma. Because of the likelihood of a long latent period for asbestos-related cancers, the risks we observed were possibly the product of since-altered occupational and environmental conditions existing 20-30 years ago in the asbestos-mining areas. The similarities in risks for most cancers in asbestos-mining and urban areas were noteworthy.

In plain English

This study compared cancer rates by county of residence in Quebec, Canada, using provincial tumor registry cases for 1969-73. The authors calculated age-adjusted incidence rates by cancer site and sex. They compared three counties with the largest chrysotile asbestos mines (Megantic, Richmond, Wolfe), eight surrounding counties, other mostly rural counties, and metropolitan Montreal and Quebec City. They lacked data on jobs and smoking, and accurate measures of past pollution. Among men in the mining counties, the pleural cancer rate was 8.08 times that in other rural counties, based on 3 cases. Among women there, it was 3.38 times the rural rate, based on 1 case. Men in the mining counties had 2.01 times the rural rate of peritoneal cancer, based on 2 cases. No peritoneal cases were reported among women there. Male lung cancer was only 23% above the rural rate. Montreal had the highest rates for all cancer sites combined. The authors suggested that asbestos exposures may have had a role. They cautioned that higher rates do not necessarily mean asbestos caused them, and that physicians' diagnostic habits could explain some findings.

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: Comparison of cancer incidence by county of residence (area-based study) using tumor registry data, with average annual age-adjusted incidence rates, relative risks and attributable risks
• Who was studied: Residents of Quebec Province, Canada, 1969-73, in five area groups: three asbestos-mining counties (total population 115,315: 57,685 males and 57,630 females), eight peripheral counties (419,500), other rural counties (2,560,690), metropolitan Montreal (2,509,110) and metropolitan Quebec City (423,180). Males and females were analysed separately.
• Exposure: Residence in counties containing chrysotile asbestos mines (Megantic, Richmond, Wolfe) or in surrounding counties. No individual data on occupation or exposure level were available.
• Main results:
  • Pleural cancer, males. The asbestos-mining counties had 3 cases, a rate of 1.02 per 100,000, and a relative risk of 8.08 compared with other rural counties (8 cases, rate 0.13). The peripheral counties had a relative risk of 2.21. The attributable risk in the mining counties was 87.6.
  • Pleural cancer, females. The asbestos-mining counties had 1 case, a rate of 0.35 per 100,000, and a relative risk of 3.38 compared with other rural counties (6 cases, rate 0.10).
  • Peritoneal cancer, males: the asbestos-mining counties had 2 cases, a rate of 0.64 per 100,000, and a relative risk of 2.01 compared with other rural counties.
  • Females in the asbestos-mining counties: no mediastinal or peritoneal cancer cases were reported.
  • Lung cancer, males: the risk in the asbestos-mining counties was only 23% higher than in rural counties. Urban rates were substantially higher.
  • Colon cancer: the authors did not find the higher risk reported in studies of asbestos manufacturing workers.
  • Melanoma: females in the mining counties had a relative risk of 2.5. This was not seen among males.
  • Attributable risk, males: about 50% of the male risk for cancer of the peritoneum, lip, tongue and salivary gland was statistically attributable to residence in the asbestos-mining counties. The figure was 71% for the small intestine and almost 90% for the pleura.
  • All cancer sites combined: Montreal had the highest rates, Quebec City the next highest, and other rural areas the lowest. The asbestos-mining and surrounding counties were in between.
  • Metropolitan populations had a risk about as high as the mining counties for every cancer site except the pleura.
• The authors' conclusion: The authors suggested that occupational and other asbestos exposures may have had a role in the higher risks. They stated that a higher risk in the mining areas does not necessarily mean asbestos produced it. They wrote that the observed risks were likely the product of exposures 25-30 years earlier, and that concluding today's populations are at higher risk would possibly be an error.
• Limitations the authors state:
  • No data on the occupations of the populations studied.
  • No accurate information on air or water pollution levels in the study areas for 1969-73. Knowledge of pollution over the previous 40 years was scanty and rested mainly on residents' accounts.
  • The completeness of reporting to the tumor registry had not been verified.
  • Higher rates in the mining counties could reflect different diagnostic habits of physicians there.
  • Many rates were based on small numbers of cases.
  • No smoking data, so the authors could not examine lung cancer risk related to smoking.
  • Other traits of the population near the mines, rather than asbestos, could be responsible for the higher risks.

Topics

Medical terms in this study, explained in our Lexicon: Cancer Registry, Relative Risk, Pleura, Peritoneum.

Related studies

• Long-term mortality experience of chrysotile miners and millers in Thetford Mines, Quebec — W.J. Nicholson, I.J. Selikoff, et al. (1979)
• Environmental pleural plaques in residents of a Quebec chrysotile mining town — A. Churg, L. DePaoli (1988)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• Mortality from cancer and other causes in the Balangero cohort of chrysotile asbestos miners — E. Pira, C. Pelucchi, et al. (2009)
• Cancer incidence among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2015)
• Dust exposure and mortality in chrysotile mining, 1910-75 — J.C. McDonald, F.D. Liddell, et al. (1980)

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