Estimate of the fraction of cancer in the United States related to occupational factors

Our plain-English summary of Estimate of the fraction of cancer in the United States related to occupational factors, by National Cancer Institute (1978).

The study

• Author: National Cancer Institute
• Published: National Cancer Institute (1978)
• Type of article: Government report
• Our copy: from Johns-Manville's own medical library.

In plain English

This 1978 report by scientists at the National Cancer Institute, National Institute of Environmental Health Sciences and National Institute for Occupational Safety and Health was not a new study. It used published data and government estimates to project the share of US cancer related to work exposures. For asbestos, it used an estimate that 8 to 11 million US workers had been exposed since World War II, about 4 million of them heavily. Citing earlier worker studies, it stated that 35-44% of heavily exposed workers who had died had died of lung cancer, pleural or peritoneal mesothelioma, or gastrointestinal cancers. It projected 2.0 to 2.3 million asbestos-related cancers. That averaged 58,000 to 75,000 cancer deaths a year over 30-35 years, or 13-18% of expected US cancer deaths. A cruder one-cohort method, counting only the roughly 1.6 million currently exposed asbestos workers, projected 13,900 asbestos cancers a year (an underestimate by a factor of 4-5, the authors said) and about 33,000 for five other substances. The authors concluded that estimates of at least 20% were more reasonable. They cautioned that the figures were not precise estimates.

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: Government report reviewing earlier estimates and published studies and making numerical projections of occupationally related cancer; no new data were collected
• Who was studied: United States workers. For asbestos, an estimated 8 to 11 million workers exposed since the beginning of World War II, about 4 million of them believed to have had heavy exposure. For the other substances, numbers of exposed workers came from a 1972-74 national survey.
• Exposure: Occupational asbestos exposure (fiber types not specified), compared with five other high-exposure substances: arsenic, benzene, chromium, nickel (oxides) and petroleum fractions (including aromatics)
• Main results:
  • Citing earlier epidemiological studies (not this report's own data): of heavily exposed asbestos workers who had already died, 20-25% died of lung cancer, 7-10% of pleural or peritoneal mesothelioma and 8-9% of gastrointestinal cancers, a total of 35-44%
  • Of the 4 million heavily exposed workers, at least 1.6 million were projected to die of these asbestos-related cancers
  • Adding 0.4 to 0.7 million cancers in less heavily exposed workers (assumed to have one-quarter of the excess risk), the projected total of asbestos-related cancers was 2.0 to 2.3 million
  • Over 30-35 years, the projected average was 58,000 to 75,000 asbestos-associated cancer deaths per year, about 13-18% of the total cancer deaths expected in the United States
  • Using a simpler table method that projects excess cancers in only one cohort of currently exposed workers (about 1.6 million for asbestos), the projection for asbestos was 13,900 excess cancers per year (10,400 lung cancers plus about 3,500 mesotheliomas). The authors said this method underestimated expected asbestos mortality by a factor of 4-5. The same method gave about 33,000 cancers per year for the five other substances combined, which the authors said may likewise be underestimates.
  • The authors judged that nothing in overall US cancer statistics was inconsistent with up to 20-40% of cancers being, or becoming, attributable to occupational factors
• The authors' conclusion: The authors concluded that earlier estimates of 1% to 5% were not scientifically documented. They concluded that estimates of at least 20% of US cancer being occupationally related were much more reasonable and might be conservative, with asbestos alone probably contributing up to 13-18%.
• Limitations the authors state:
  • The table figures should not be read as precise estimates of future cancers
  • The table figures cover only one cohort of currently exposed workers, so they underestimate effects when many more workers have ever been exposed; for asbestos the underestimate is a factor of 4-5
  • The projections may overestimate cancers, because some workers exposed today may have less exposure than the workers whose risk ratios were used
  • The projections assume that relative risks stay the same for the rest of the workers' lives, even after exposure ends
  • Much of the occupational data used did not account for smoking, except for asbestos
  • The authors could not estimate future risks from present-day exposures
  • An estimate of the number of asbestos-related cancers occurring at present would be smaller than the projected future figures

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Peritoneal Mesothelioma.

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