Lung Cancer Mortality In Relation To Measured Dust Levels In An Asbestos Textile Factory

Our plain-English summary of Lung Cancer Mortality In Relation To Measured Dust Levels In An Asbestos Textile Factory, by J. Peto (1980).

The study

• Author: J. Peto
• Published: Biological Effects Of Mineral Fibres (J.C. Wagner, Editor), Lyon: Iarc Scientific Publications, Volume 30, Pp. 829-836 (1980)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library, J-M no. 002184. The article is still under copyright, so we describe it here rather than post it.

In plain English

This study followed men who worked at an asbestos textile factory and compared their deaths with the numbers expected from national death rates. It included 679 men who started work in 1933 or later and had at least 10 years of exposure by the end of 1972. They were followed to the end of 1978. Among men first exposed before 1951, there were 22 lung cancer deaths 20 or more years after first exposure, against 13.85 expected. Among the 255 men who started in 1951 or later, there were 8 such deaths against 1.62 expected, a relative risk of 4.9 (95% confidence limits 2.1 to 9.7). This later group had no deaths from asbestosis or mesothelioma, but a separate study reported 10 of them certified as having asbestosis. Revised, provisional dust estimates put this group's average cumulative exposure at 200-300 fibres/ml-years. The author concluded that the eventual lung cancer relative risk at that exposure was probably between 2 and 3. The author also found little evidence that static dust readings identified the men at high risk.

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: Cohort mortality follow-up comparing observed deaths with numbers expected from national death rates, plus a comparison of estimated cumulative exposures of 8 lung cancer cases with 42 unaffected controls
• Who was studied: 679 men who entered an asbestos textile factory in 1933 or later and had been exposed for at least 10 years by the end of 1972, followed to the end of 1978. They were split into cohort 1 (first exposed before 1951) and cohort 2 (255 men who entered from 1951 onward).
• Exposure: Asbestos dust in a textile factory (fiber type not named in this text). Area dust measurements were taken from 1951 and revised to correspond to modern fibre counting methods. Average levels were estimated at around 30 fibres/ml in 1951. The average cumulative exposure of the post-1950 cohort was estimated at 200-300 fibres/ml-years.
• Main results:
  • Men first exposed before 1951 (cohort 1): 22 lung cancer deaths 20 or more years after first exposure, compared with 13.85 expected (P less than 0.05)
  • Later employees (cohort 2): 8 lung cancer deaths compared with 1.62 expected (P less than 0.001)
  • Relative risk for lung cancer 20 or more years after first exposure in post-1950 employees was 4.9 (95% confidence limits 2.1-9.7)
  • Assuming all men not known to have died or emigrated were alive at 31 December 1978, the observed/expected ratios were 22/14.12 (cohort 1; P less than 0.05) and 8/1.75 (cohort 2; P less than 0.001)
  • Men first employed before 1951: excess of other respiratory disease 20 or more years after first exposure (30 observed, 18.63 expected; P less than 0.01), largely accounted for by deaths attributed to asbestosis
  • Among pre-1951 employees, mesothelioma incidence rose from 0.0006 per annum at 20-25 years after first employment to 0.004 per annum beyond 35 years
  • No deaths in cohort 2 were attributed to asbestosis or mesothelioma; 1.9 asbestosis and 0.4 mesothelioma deaths would have been expected from cohort 1 rates. A separate study reported 10 of these men certified as asbestotic.
  • Both cohorts: 14 deaths from gastrointestinal cancers (12.60 expected); no peritoneal mesothelioma occurred
  • The 8 lung cancer cases (all cigarette smokers) showed no evidence of anomalously heavy exposures compared with 42 controls who entered the factory between 1951 and 1955
• The authors' conclusion: The author concluded that the eventual relative risk for lung cancer among men with estimated cumulative exposures of about 200-300 fibres/ml-years is probably between 2 and 3. The author also found little evidence that 2- to 3-fold variations in static sample measurements discriminate those at high risk.
• Limitations the authors state:
  • The number of deaths was too small for precise estimates
  • The revised dust estimates are based on preliminary data and are provisional
  • Individual exposure estimates are inevitably inaccurate
  • The apparently marked increase in lung cancer risk in post-1950 employees is likely largely due to chance
  • 41 untraced men were assumed alive at the previous follow-up date, which may have exaggerated the risk
  • No routine dust measurements were made before 1951, so earlier dust estimates are speculative
  • The absence of asbestosis and mesothelioma deaths in later employees may reflect their short follow-up

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Relative Risk, Mesothelioma, Cumulative Exposure.

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