Validation Of The Uicc/Cincinnati Classification Of Radiographs In Terms Of Prediction Of Mortality Of Asbestos Workers

Our plain-English summary of Validation Of The Uicc/Cincinnati Classification Of Radiographs In Terms Of Prediction Of Mortality Of Asbestos Workers, by F.D.K. Liddell (1980).

The study

• Author: F.D.K. Liddell
• Published: Biological Effects Of Mineral Fibres (J.C. Wagner, Editor), Lyon: Iarc Scientific Publications, Volume 30, Pp. 667-671 (1980)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library, J-M no. 002180. The article is still under copyright, so we describe it here rather than post it.

In plain English

This paper reported part of a project asking how well chest X-ray changes predicted death in asbestos workers. The author studied 4559 men from the Quebec chrysotile mines and mills whose last X-ray while employed had been read in 1967 under the forerunner of the UICC/Cincinnati classification, and grouped them as 'normal' or 'less-than-normal'. By the end of 1975, 1543 had died. For deaths from all causes, the relative risk for 'less-than-normal' compared with 'normal' men was 1.74. It was 11.75 for pneumoconiosis (31 deaths) and 3.24 for lung cancer (118 deaths). Among the lung cancer deaths, films were more often 'normal' the longer the gap between last job and death: 19% when the gap was under five years and 70% when it was over 20 years. All five mesothelioma deaths were pleural. The three men who died within about a year of their X-ray had 'less-than-normal' films. The author stated that no claim of statistical significance could be justified. The author concluded that the completed project convincingly validated the classification.

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 study using the man-years method, relating each man's last chest X-ray reading to later deaths; certain case-control studies were also carried out
• Who was studied: 4559 men from the cohort of 11,379 persons born 1891 to 1920 who had worked at least one month in the Quebec mines and mills. Each man had had at least one postero-anterior chest X-ray while still employed, and the last one had been read in 1967 by one of six readers. 603 men eligible for another study group were excluded. By the end of 1975, 1543 had died (33.8%), 2957 had survived and 59 were lost to view (1.3%).
• Exposure: Work in Quebec chrysotile mines and mills. Radiographic findings were classified by the forerunner of the UICC/Cincinnati classification. Accumulated dust exposure (millions of particles per cubic foot times years) and smoking habits were also analysed.
• Main results:
  • All causes: 791 deaths among 'normals' (SMR 1.20) and 636 among 'less-than-normals' (SMR 2.08), giving a relative risk of 1.74; the relative risks took age differences into account
  • Relative risks for all-cause deaths calculated separately for the six X-ray readers were 1.41, 1.55, 1.68, 1.88, 2.00 and 2.01
  • Relative risks for all-cause deaths for specific X-ray features, compared with 'normals': small opacities 1.98; large opacities 4.43; uncalcified pleural changes 1.87; pleural calcification 1.62; 'additional symbols' 2.21
  • Pneumoconiosis: among 31 deaths, parenchymal change had been recorded in 23 (74.2%) and five films were 'normal'. The relative risk in 'less-than-normals' was 11.75.
  • Lung cancer (118 deaths): the relative risk in 'less-than-normals' was 3.24
  • Lung cancer: 40.7% of the 118 lung cancer deaths had 'normal' films, compared with 16.1% of pneumoconiosis deaths
  • Among lung cancer deaths, the share of 'normal' films rose with the interval between last recorded job and death: 9/48 (19%) under 5 years; 16/36 (44%) at 5 to under 10 years; 9/14 (64%) at 10 to under 20 years; 14/20 (70%) over 20 years
  • Large opacities had been recorded in 14 lung cancer cases, six of them without a background of small opacities. In 11 of the 14, the interval between last job and death was under five years.
  • Five deaths were due to malignant mesothelioma, all of the pleura. The three men who died within about a year of their X-ray all had 'less-than-normal' films.
  • Of the other two mesothelioma cases, whose films were taken five and nine years before death, one was read as p, 1/0 and one as 'normal'
  • The case-control study showed the expected enhanced risk due to smoking and a minor excess risk due to dust exposure
• The authors' conclusion: The author concluded that the findings of the completed project (reported more fully elsewhere) convincingly validated the UICC/Cincinnati classification. The abnormality on X-ray was not specific to lung cancer, except for 'large opacities'.
• Limitations the authors state:
  • Many chi-square values were computed and the subcohorts overlapped, so the author stated that no statement of statistical significance can be justified
  • The proportion of 'less-than-normal' films ranged from 20.9% to 39.9% across the six readers' sets, which the author attributed almost certainly to observer variation

Topics

Medical terms in this study, explained in our Lexicon: UICC, Chest X-Ray, Quebec Chrysotile, Relative Risk, Pneumoconiosis, Lung Cancer, Mesothelioma, Statistical Significance.

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