Methodological problems in ecologic studies of the asbestos--cancer relationship

Our plain-English summary of Methodological problems in ecologic studies of the asbestos--cancer relationship, by S. Graham (Environmental Research, 1981).

The study

• Author: S. Graham
• Journal: Environmental Research
• Published: 1981;25(1):35-49
• Cited by: 6 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. 000741).

In plain English

This ecologic study used Quebec's Provincial Tumor Registry to compare age-adjusted cancer incidence, 1969-1973, by sex and cancer site. It compared the three asbestos-mining counties, the surrounding counties, other rural counties, Montreal and Quebec. Exposure was defined by residence, not measured individually. Compared with men in other rural counties, men in the asbestos counties had higher risks of cancer of the pleura (3 cases, relative risk 8.08), peritoneum, lip, tongue, salivary gland and small intestine. Women there, compared with women in other rural counties, had higher risks of cancer of the lip (3 cases, relative risk 8.76), pleura (1 case), kidney, salivary gland and melanoma. For several cancers, risk rose with closeness to the mines. Lung, stomach and colon cancer were raised only at a level the author called unimpressive. The author cautioned that the design gives no direct knowledge of whether people with cancer actually had contact with asbestos, and smoking data were unavailable. The author added that the registry may be incomplete or biased, and that the cancers studied probably reflected exposures many years earlier, so the risks may not apply to current exposure.

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: Ecologic study comparing cancer incidence rates from a population-based tumor registry across groups of counties
• Who was studied: All registered cancer cases in Quebec, 1969-1973, by sex. Areas compared: the three asbestos-mining counties (57,685 males; 57,630 females), peripheral counties (209,320 males), other rural counties (1,295,895 males), Montreal (1,227,245 males) and Quebec (204,435 males).
• Exposure: Residence in or near asbestos-mining counties, including the towns of Asbestos and Thetford Mines, where mine tailings containing some asbestos lay in and around the towns. No individual exposure data were available, and the article does not specify a fiber type for this study.
• Main results:
  • The comparison population for the relative risks was the rural non-mining counties. The tabulated relative risks match each area's rate divided by the 'other rural counties' rate.
  • Compared with other rural counties, males in asbestos-mining counties had higher risks of cancer of the pleura, peritoneum, lip, tongue, salivary gland and small intestine.
  • Pleural cancer, males in asbestos counties: 3 cases, rate 1.02 per 100,000, relative risk 8.08 compared with other rural counties.
  • Pleural cancer, males: 8 cases (rate 0.13) in other rural counties and 3 cases (rate 0.28) in peripheral counties, with a relative risk of 2.21 for the peripheral counties.
  • Lip cancer, males in asbestos counties: 31 cases, rate 10.59, relative risk 1.90 compared with other rural counties.
  • Compared with other rural counties, females in asbestos-mining counties had higher risks of cancer of the pleura, lip, kidney, salivary gland, and melanoma.
  • Lip cancer, females in asbestos counties: 3 cases, rate 1.08, relative risk 8.76 compared with other rural counties.
  • Pleural cancer, females in asbestos counties: 1 case, rate 0.35, relative risk 3.38 compared with other rural counties.
  • Risks increased with proximity to the mines.
  • Colon, stomach and lung cancer were also raised, but only at a low level. For lung cancer, males in asbestos counties had 97 cases, rate 33.59, relative risk 1.23 compared with other rural counties.
  • A comparison of 1969 male cancer rates between the Quebec registry and upstate New York showed broadly similar rates.
• The authors' conclusion: The author concluded that earlier findings on mesothelial tumors were corroborated and that new relationships were suggested for lip, tongue, salivary gland, small intestine and kidney cancer. The author cautioned that the risks found may not be associated with current exposure.
• Limitations the authors state:
  • The ecologic design gives no direct knowledge of whether the people who developed cancer actually had contact with asbestos.
  • No data on smoking, actual occupational or residential exposure, or pollution were available in the registry.
  • Long latency, during which mining practices and pollution controls changed, makes the study an inadequate basis for testing causal hypotheses.
  • The results reflect exposures from as many as twenty years earlier and may not be associated with current exposure.
  • The Quebec registry was probably less complete than the roughly 90% completeness found for the New York registry.
  • Doctors in mining counties may have been more inclined to report pleural cancer.
  • Expected numbers of specific cancers per county were very small.

Related studies

• Comment on 'The latency period of mesothelioma among a cohort of British asbestos workers (1978-2005)': methodological problems with case-only survival analysis — D. Consonni, F. Barone-Adesi, et al. (2014)
• Cancer in asbestos-mining and other areas of Quebec — S. Graham, M. Blanchet, et al. (1977)
• Methodological issues in descriptive environmental epidemiology. The example of study Sentieri — C. Ciocan, N. Franco, et al. (2021)
• Mesothelioma in occupational cohort studies: methodological considerations — N.C. Wojcik, A.R. Schnatter, et al. (2014)
• Human cancer risk from ingested asbestos: a problem of uncertainty — W.J. Nicholson (1983)
• A case-control study of asbestos in drinking water and cancer risk — L. Polissar, R.K. Severson, et al. (1984)

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