Occupational cancer: experience in Ontario

Our plain-English summary of Occupational cancer: experience in Ontario, by A.C. Chovil, W.J. McCracken, E.C. Dowd, et al (Canadian Medical Association Journal, 1981).

The study

• Authors: A.C. Chovil, W.J. McCracken, E.C. Dowd, C. Stewart, D.F. Burton, D.W. Dyer
• Journal: Canadian Medical Association Journal
• Published: 1981;125(11):1237-41
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

This paper reviews the experience of the Workmen's Compensation Board of Ontario in identifying cases of cancer that could be attributed to occupational hazards. Worker's claims for compensation are allowed if there is reasonable medical evidence that their cancer was caused by exposure to risk factors associated with their occupation. Details of the types of cancer associated with specific carcinogens or fields of employment are discussed. About 50% of the cases were related to exposure in particular industrial operations that functioned for relatively brief periods. The number of deaths from cancer identified as being caused by occupational factors is compared with the total for cancer from all causes in Ontario during the period 1971 through 1975. Although all workers eligible for compensation may not have been identified, the data suggest that less than 1% of cancer is presently caused by occupational factors.

In plain English

This article reviewed accepted claims at the Workmen's Compensation Board of Ontario for cancers diagnosed up to the end of 1978. The authors called their data anecdotal rather than epidemiologic, and rejected claims were not included. About half of the claims involved nickel refining or arsenic smelting processes that had stopped by early 1963. Most of the asbestos the claimants used was believed to have been chrysotile, with crocidolite also used. Asbestos-related claims were accepted for 38 workers with primary lung cancer, 32 with mesothelioma (23 pleural, 9 peritoneal), 7 with gastrointestinal cancer and 3 with laryngeal cancer. Some mesothelioma claims involved light, brief or long-past exposure. Among Ontario males in 1971 through 1975, deaths in workers with accepted occupational claims were 0.34% of all cancer deaths (111 of 32194) and 0.89% of lung cancer deaths (84 of 9 334). The longest latency observed for mesothelioma was 44 years. The authors concluded that 1% or less is probably a good estimate of the share of cancer in Ontario caused by occupational hazards. They acknowledged that case identification was incomplete.

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 a workers' compensation board's records of accepted cancer claims; the authors describe the data as anecdotal rather than epidemiologic
• Who was studied: Workers in Ontario (population 8.5 million, work force 4.3 million) whose cancer was diagnosed up to the end of 1978 and whose compensation claims were accepted by the Workmen's Compensation Board of Ontario before the end of 1979; 427 cases in Table I (1947 through 1978)
• Exposure: Several occupational carcinogens (nickel refinery processes, asbestos, ionizing radiation mainly from uranium, coal tar and hydrocarbons, arsenic, aniline dyes). For asbestos, mostly chrysotile was believed to have been used, with crocidolite also used in some processes; jobs included drywall construction, pipe fitting, brake lining manufacture, shipyards, processing and insulation trades
• Main results:
  • About half of all accepted claims were for cancer linked to specific nickel refining or arsenic smelting processes discontinued by early 1963
  • Among asbestos-exposed workers, claims were accepted for 38 workers with primary lung cancer
  • Of 32 accepted mesothelioma claims in asbestos-exposed workers, 23 were pleural and 9 peritoneal
  • Some mesothelioma claims were allowed where exposure was deemed relatively light, short, or in the distant past, including two workers who manufactured gas mask canisters during World War II
  • Other accepted claims in asbestos-exposed workers were for 7 with gastrointestinal cancer and 3 with laryngeal cancer
  • Ontario males, 1971 through 1975: 111 deaths in workers with accepted occupational claims out of 32194 deaths from all types of cancer (0.34%)
  • Ontario males, 1971 through 1975: 84 occupational lung cancer deaths out of 9 334 lung cancer deaths from all causes (0.89%)
  • Ontario males, 1971 through 1975: 12 occupational nasal sinus cancer deaths out of 87 (13.79%)
  • The longest latency periods observed were 50 years for nasal sinus cancer and 44 years for mesothelioma
• The authors' conclusion: The authors concluded that a proportion of 1% or less is probably a good estimate of how much occupational hazards contribute to cancer in Ontario at present
• Limitations the authors state:
  • Identification of cases will be incomplete
  • Because guidelines give the benefit of the doubt to the patient, accepted claims may include some cancers that were actually not occupational
  • Rejected claims were excluded, so accepted and rejected claims cannot be meaningfully compared
  • There were some defects in the early records

Related studies

• Analysis of mortality patterns and workers' compensation awards among asbestos insulation workers in Ontario — M.M. Finkelstein (1989)
• Occupational associations with lung cancer in two Ontario cities — M.M. Finkelstein (1995)
• An approach to estimating the environmental burden of cancer from known and probable carcinogens: application to Ontario, Canada — S.L. Greco, E. MacIntyre, et al. (2020)
• Exploring the usefulness of occupational exposure registries for surveillance: the case of the Ontario Asbestos Workers Registry (1986-2012) — A.J. Koné Pefoyo, L. Genesove, et al. (2014)
• Filing for workers' compensation among Ontario cases of mesothelioma — J.I. Payne, E. Pichora (2009)
• Occupational lung cancer and smoking: a review in the light of current theories of carcinogenesis — A.C. Chovil (1979)

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