Respiratory cancer in relation to occupational exposures among retired asbestos workers

Our plain-English summary of Respiratory cancer in relation to occupational exposures among retired asbestos workers, by P. Enterline, P. de Coufle, V. Henderson (British Journal of Industrial Medicine, 1973).

The study

• Authors: P. Enterline, P. de Coufle, V. Henderson
• Journal: British Journal of Industrial Medicine
• Published: 1973;30(2):162-6
• Cited by: 52 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001302).

Abstract

Enterline, P., de Coufle, P., and Henderson, V. (1973).British Journal of Industrial Medicine,30, 162-166. Respiratory cancer in relation to occupational exposures among retired asbestos worker. A cohort of 1 348 men who completed their working lifetime in the asbestos industry and retired with an industry pension during the period 1941-67 was observed through 1969 for deaths. The average length of employment in the asbestos industry for these men was 25 years and all had exposures to asbestos dust. In some instances these exposures were very high and continued for many years. Mortality for this cohort of men after age 65 was 14·7% higher than for the entire population of United States white men living at the same ages and time periods. This excess was due almost entirely to cancer and respiratory disease. The cancer excess was chiefly due to respiratory cancer where mortality was 2·7 times the expected. The respiratory disease excess was entirely due to asbestosis. A time-weighted measure of asbestos dust exposure at the time of retirement was calculated for each man. This was made up of the summed products of dust levels for each job (expressed in mppcf) and years at each level. This measure was directly related to the respiratory cancer excess at ages 65 and over, ranging from 1·7 times expected for men with less than 125 mppcf-years exposure to 5·6 times expected for men with 750 or more mppcf-years exposure. There appeared to be no direct relationship between asbestos dust exposure and respiratory cancer below 125 mppcf-years. Important increments in respiratory cancer mortality apparently occurred somewhere between 100 and 200 mppcf-years exposure. Separation of the effects of time from the effects of average dust level on respiratory cancer mortality showed that the contribution of each was about the same and that a time-weighted measure of asbestos dust appears to be an appropriate method for predicting respiratory cancer effects.

In plain English

This study followed 1,348 men who had worked as production or maintenance employees in the US asbestos industry, retired with an industry pension between 1941 and 1967, and reached age 65. Their deaths were tracked through 1969. The article does not name the asbestos fiber types involved. Each man's cumulative exposure was estimated as dust level (million particles per cubic foot of air, mppcf) multiplied by years worked, giving mppcf-years. Compared with all US white men of the same ages and periods, the retirees had 754 deaths against 657.2 expected (SMR 114.7). There were 58 respiratory cancer deaths against 21.7 expected (SMR 267.3), and 18 deaths were due to asbestosis. Respiratory cancer rose with cumulative exposure. The SMR was 166.7 for 533 men under 125 mppcf-years, and respiratory cancer deaths were 5.6 times the expected number for the 56 men at 750 or more mppcf-years. Within the under-125 group, no direct relationship appeared. Exposure time and dust level predicted respiratory cancer about equally well. The authors concluded that large increases appeared somewhere between 100 and 200 mppcf-years. They noted that the dust estimates were very crude and the numbers often very small.

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: Retrospective cohort mortality study of retirees, comparing observed deaths with deaths expected from the US white male population (modified life table method)
• Who was studied: 1,348 men (of 1,376 who reached age 65) who were production or maintenance employees in the US asbestos industry, retired with an industry pension in 1941-67 and were followed for deaths through 1969. Average employment was 25 years (range 3 to 51 years).
• Exposure: Asbestos dust (fiber type not specified), estimated for each job and time period in million particles per cubic foot of air (mppcf) using six rough classes, and summed as cumulative mppcf-years at retirement
• Main results:
  • Whole cohort: 754 deaths observed versus 657.2 expected (SMR 114.7), an overall mortality 14.7% higher than US white males
  • Whole cohort: respiratory cancer had the greatest cancer excess, with 58 observed versus 21.7 expected (SMR 267.3). All cancers: 167 observed versus 109.4 expected (SMR 152.6).
  • Whole cohort: respiratory disease deaths were 67 versus 36.8 expected (SMR 182.1). The excess was due entirely to pneumoconiosis and pulmonary fibrosis (29 deaths), of which 18 were asbestosis.
  • Respiratory cancer rose with total dust exposure. SMRs by exposure group: 166.7 for 533 men under 125 mppcf-years (15 observed, 9.0 expected); 250.0 for 305 men at 125-249; 326.9 for 328 men in the next band; 500.0 for 126 men at 500-749. For the 56 men at 750 and over there were 5 observed versus 0.9 expected. That SMR is printed '555 6' in the scanned table; 5 divided by 0.9 gives 555.6, and the authors' abstract gives 5.6 times expected.
  • Among the 533 men under 125 mppcf-years, no direct dust-response relationship appeared. SMRs were 153.8 (under 25), 258.1 (25.0-62.4) and 108.7 (62.5-124.9); the relationship appeared slightly inverse.
  • Correcting for urban residence reduced the respiratory cancer SMR for men under 125 mppcf-years from 166.7 to 146.2
  • In a parallel study of 324 male retirees from building materials manufacture exposed to non-asbestos dust, there were 9 respiratory cancer deaths versus 5.3 expected (SMR 169.8)
  • Duration of exposure and average dust level together correlated with respiratory cancer SMR (R = 0.850, printed '0 850'). Time at fixed level (r = 0.738) predicted nearly as well as level at fixed time (r = 0.772).
• The authors' conclusion: The authors concluded that large increases in respiratory cancer appear at a cumulative asbestos dust exposure somewhere between 100 and 200 mppcf-years. They also concluded that a time-weighted dust measure appears appropriate for predicting respiratory cancer effects.
• Limitations the authors state:
  • Estimates of past dust levels were very crude, and numbers were in many instances very small
  • Dust levels could only be roughly classified
  • Death certificates were located for only 733 of the 754 deaths
  • Expected deaths were based on the entire US, but the men were mainly urban dwellers, so expected respiratory cancer deaths may be too low
  • Whether the SMR of 166.7 in the lowest exposure group is related to asbestos dust or to something else could not be established
  • The meaning of exposure time is uncertain; it may reflect increasing dose, a longer latent period, or both

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Million Particles per Cubic Foot (mppcf).

Related studies

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• Estimating the social cost of respiratory cancer cases attributable to occupational exposures in France — H. Serrier, H. Sultan-Taieb, et al. (2014)
• Past occupational dust exposure, depressive symptoms and anxiety in retired Chinese factory workers: the Guangzhou Biobank Cohort Study — Q.H. Lin, C.Q. Jiang, et al. (2014)
• Occupational respiratory cancer and exposure to asbestos: a case-control study in a cohort of workers in the electricity and gas industry — E. Imbernon, M. Goldberg, et al. (1995)
• Respiratory cancer incidence in Swedish construction workers exposed to man-made mineral fibres and asbestos — G. Engholm, A. Englund, et al. (1987)
• Respiratory carcinogenesis: an epidemiologic appraisal — J.F. Fraumeni (1975)

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