Radiographic asbestosis is not a prerequisite for asbestos-associated lung cancer in Ontario asbestos-cement workers

Our plain-English summary of Radiographic asbestosis is not a prerequisite for asbestos-associated lung cancer in Ontario asbestos-cement workers, by M.M. Finkelstein (American Journal of Industrial Medicine, 1997).

The study

• Author: M.M. Finkelstein
• Journal: American Journal of Industrial Medicine
• Published: 1997;32(4):341-8
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In recent years, controversy has developed about whether pre-existing asbestosis is a prerequisite for the diagnosis of asbestos-related lung cancer. This paper presents the results of a prospective study, in a cohort of Ontario asbestos-cement workers, of lung cancer in relation to radiographs obtained 20 and 25 years from first exposure to asbestos. Radiographs were interpreted by a single NIOSH-certified "B" reader, and asbestosis was defined to mean an ILO code of 1/0 or greater. There were 143 subjects (123 without asbestosis, 20 with asbestosis), with a radiograph available for interpretation at 20 years from first exposure or later. The lung cancer standardized mortality ratio (SMR) among men without asbestosis at 20 years latency was 5.53 (95% CI: 2.9-9.7). There were 128 subjects (114 without asbestosis, 14 with asbestosis) with a radiograph available for interpretation at 25 years from first exposure or later. The lung cancer SMR among men without asbestosis at 25 years latency was 5.81 (95% CI 2.7-11). The results of this study are consistent with those of epidemiologic studies of asbestos-exposed populations in a variety of exposure situations. These studies have demonstrated that lung cancer risk is elevated in the presence of radiographic asbestosis, but they have also shown that lung cancer risk may be elevated in the absence of radiographic asbestosis.

In plain English

This study followed men from an asbestos–cement factory in Scarborough, Ontario, which made pipe and board from chrysotile and crocidolite asbestos, silica and cement. The 151 men studied were production workers hired before 1960 who had at least one chest X-ray available. Deaths were tracked to the end of 1985 and compared with the general population of Ontario. A single certified reader classified the X-rays, defining asbestosis as small irregular opacities at ILO category 1/0 or more. Among men without asbestosis on X-rays from 20 years after first exposure, lung cancer deaths were 5.53 times the expected number (95% confidence interval 2.9 to 9.7). At 25 years the figure was 5.81 (2.7 to 11). Men with asbestosis had ratios almost twice as high, but the difference between the two groups was not statistically significant, because the groups were small. Smokers and men who said they had never smoked had similar lung cancer ratios. The author concluded that workers without radiographic asbestosis had a significantly increased lung cancer risk compared with the general population.

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: Prospective cohort mortality study comparing workers classified by chest X-ray with the general population of Ontario (standardized mortality ratios), plus internal Cox regression analyses
• Who was studied: Production workers at an asbestos–cement factory in Scarborough, Ontario (opened 1948), hired before 1960, employed 9 years or more, with at least 12 months in asbestos exposure. 186 men were eligible and 151 with at least one radiograph were studied. Mortality was followed to the end of 1985.
• Exposure: Work manufacturing asbestos–cement pipe and board from chrysotile and crocidolite asbestos, silica and cement. Cumulative asbestos exposure was estimated in fiber-years/ml from a model; silica exposure was not estimated.
• Main results:
  • Using X-rays at 20 years from first exposure (143 men: 123 without asbestosis, 20 with), the lung cancer SMR among men without asbestosis was 5.53 (95% CI 2.9 to 9.7).
  • Using X-rays at 25 years from first exposure (128 men: 114 without asbestosis, 14 with), the lung cancer SMR among men without asbestosis was 5.81 (95% CI 2.7 to 11).
  • At both 20 and 25 years, the lung cancer SMR among men with asbestosis was almost twice as high (9.96 and 9.20 in Table I), but the confidence intervals overlapped and there was no significant difference between men with and without asbestosis.
  • At 30 years, only 33 men were available (15 without asbestosis, 18 with). There were no lung cancer deaths among men without asbestosis (0.25 expected). There were two among men with asbestosis, an SMR of 7.46 that was not statistically significant.
  • Lung cancer SMRs did not differ between smokers (14 observed, 2.18 expected, SMR 6.44) and men reporting they never smoked (3 observed, 0.49 expected, SMR 6.18).
  • In Cox regression of age, asbestosis, smoking and cumulative exposure, only age was significantly associated with lung cancer risk. In the time-dependent analysis, the relative risk for men with asbestosis compared with men without was 2.3, which was not statistically significant (P = 0.15).
  • Lung cancer SMRs suggested an increase with cumulative exposure, but there were no significant differences among the exposure groups.
• The authors' conclusion: The author concluded that asbestos–cement workers without radiographic asbestosis had a significantly increased lung cancer risk compared with men in the general population. Drawing on this and other studies, the author concluded that radiographic asbestosis is not a prerequisite for asbestos-associated lung cancer.
• Limitations the authors state:
  • The small number of men produced wide confidence intervals and prevented detecting differences between groups.
  • Deaths from other asbestos-related causes (mesothelioma, gastrointestinal cancer, asbestosis) competed with lung cancer and affected the observed rates.
  • X-rays were read by a single reader; the author raised the possibility that other readers might have coded some films as asbestosis.
  • Film quality was variable, since most films came from routine surveys.
  • The author suspected that the men with lung cancer who reported never smoking were misclassified.
  • No estimates of silica exposure were available.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Asbestos-Cement, NIOSH, standardized mortality ratio (SMR), Latency.

Related studies

• Absence of radiographic asbestosis and the risk of lung cancer among asbestos-cement workers: Extended follow-up of a cohort — M.M. Finkelstein (2010)
• Regarding "absence of radiographic asbestosis and the risk of lung cancer among asbestos-cement workers: extended follow-up of a cohort", by Murray Finkelstein, American Journal of Industrial Medicine 2010 — R.M. Ross (2011)
• Mortality among employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1984)
• Mortality among long-term employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1983)
• Asbestosis in long-term employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1982)
• Survival in cohorts of asbestos cement workers and controls — M. Albin, V. Horstmann, et al. (1996)

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