Asbestos and cancer: a cohort followed up to death

Our plain-English summary of Asbestos and cancer: a cohort followed up to death, by P.E. Enterline, J. Hartley, V. Henderson (British Journal of Industrial Medicine, 1987).

The study

• Authors: P.E. Enterline, J. Hartley, V. Henderson
• Journal: British Journal of Industrial Medicine
• Published: 1987;44(6):396-401
• Cited by: 117 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. 000313).

Abstract

The mortality experience of 1074 white men who retired from a United States asbestos company during the period 1941-67 and who were exposed to asbestos working as production and maintenance employees for the company is reported to the end of 1980 when 88% of this cohort was known to be dead. As noted in earlier reports the mortality for respiratory and gastrointestinal cancer was raised. A more detailed examination of causes of death shows that the excess in gastrointestinal cancer was largely due to a statistically significant excess in stomach cancer. A statistically significant excess was also noted for kidney cancer, cancer of the eye, and non-malignant respiratory disease. Eight deaths from malignant mesothelioma were observed, two of which were peritoneal. Asbestos exposures for these mesothelioma cases were low relative to other members of the cohort. Continuing follow up of this cohort shows a dose response relation for respiratory cancer that has become increasingly linear. Standardised mortality ratios peaked 10 to 15 years after retirement and were relatively constant at around 250 in each five year interval starting in 1950. This excess might have been detected as early as 1960 but certainly by 1965. The mortality experience of this cohort reflects the ultimate effects of asbestos since nearly all of the cohort has now died.

In plain English

This study followed 1,074 white men who retired between 1941 and 1967 from a United States asbestos products company after working in production or maintenance jobs. Their deaths were tracked to the end of 1980, when 944 (88%) were known to have died. Compared with US white men's death rates, the retirees had more deaths than expected overall. There were also excess deaths from respiratory cancer, stomach cancer, kidney cancer, eye cancer (two deaths), tuberculosis and non-malignant respiratory disease. Eight mesothelioma deaths were identified from death certificates (one marked only as possibly mesothelioma), two of them peritoneal. These men did not have unusually high exposure compared with others in their departments. Respiratory cancer rose with estimated cumulative dust exposure, from a standardised mortality ratio of 182.3 in the lowest exposure group to 698.7 in the highest (100 means deaths as expected). The authors concluded that asbestos exposure had undoubtedly played an important part in the high death rates, and that the cancer excess might have been detected as early as 1960. They noted small numbers and uncertain causes of death at the oldest ages.

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: an update to 1980 of earlier reports on retirees of one company. Observed deaths were compared with deaths expected from US white male death rates, expressed as standardised mortality ratios (SMRs).
• Who was studied: 1,074 men who retired in 1941-67 from a large US asbestos products company (the acknowledgments name the Johns Manville Corporation) after working as production or maintenance employees. Average employment was 25 years (range 3-51). Follow-up began at age 65, or at retirement if later, and ran to the end of 1980.
• Exposure: Asbestos dust in the company's operations. Each worker's exposure was estimated in million particles per cubic foot from hygiene surveys that began in the mid-1950s and were extrapolated back in time. Cumulative exposure was expressed in mppcf-years. Each worker was assigned a primary fiber type (chrysotile, amosite or crocidolite is given for the mesothelioma cases).
• Main results:
  • By the end of 1980, 944 of the 1,074 men were known to be dead, and death certificates were found for 910. Of the 130 presumed alive, 99 were verified as alive and 31 could not be located.
  • The excess of digestive cancer seen in earlier reports was largely due to stomach cancer, which had a statistically significantly raised SMR.
  • There was an excess of kidney cancer not noted in earlier reports. There was also a statistically significant excess of eye cancer, based on only two deaths.
  • Death rates from tuberculosis and non-malignant respiratory disease were high. The authors attributed the non-malignant respiratory excess largely to asbestos-related deaths and said the reason for the tuberculosis excess was not clear.
  • Eight mesothelioma deaths were identified from death certificates, slightly under 1% of all deaths. Five were pleural (one marked 'possibly mesothelioma'), two peritoneal and one unspecified. The primary fiber type was chrysotile for six men, amosite for one (an insulation worker with peritoneal mesothelioma) and crocidolite for one. The longest apparent latency was 55 years.
  • The men who died of mesothelioma did not have unusually high asbestos exposure compared with all retirees from their departments. The authors could offer no explanation for this.
  • For 1941-80 there were 79 respiratory cancer deaths, with an SMR of 258.4.
  • Respiratory cancer SMRs rose with cumulative exposure. In the highest exposure group (over 750 mppcf-y) there were 8 deaths and an SMR of 698.7 for 1941-80. In the lowest group (under 125 mppcf-y) there were 23 deaths and an SMR of 182.3.
  • The dose-response line for respiratory cancer to 1980 was SMR = 116.5 + 0.56 (mppcf-y), compared with SMR = 100 + 0.66 (mppcf-y) in the follow-up to 1973. The authors described the slope as having diminished slightly, 'although perhaps not significantly'.
  • By age, the respiratory cancer SMR was highest at ages 75-79: 28 observed against 7.05 expected deaths, SMR 397.1. At 80-84 the SMR was 99.7 (3 deaths) and at 85 and over it was 125.3 (1 death).
  • Over time, respiratory cancer SMRs stayed relatively constant from 1950 to 1980, while the absolute excess death rate rose sharply. The authors linked this to rising background respiratory cancer rates in the US.
  • The excess of respiratory cancer might have been detectable by 1960, when 12 deaths had occurred against about five expected, and should have been clear by the end of 1964.
• The authors' conclusion: The authors concluded that overall death rates in these retirees were high and that asbestos exposure had undoubtedly played an important part in this. They also suggested that monitoring retired populations could be useful for large organisations where a chronic disease hazard may exist.
• Limitations the authors state:
  • Numbers were small in the oldest age groups.
  • US death rates were available only for the broad group aged 85 and over, which may not be the correct comparison for this population.
  • The cause of death in the very old is often uncertain.
  • Some workers may have been exposed to more than one type of asbestos, even if their primary job involved only one type.
  • Some asbestosis or other asbestos-related lung conditions may have been misclassified as tuberculosis.
  • Only men who reached retirement were studied, and it is unknown whether workers who left earlier had different mortality.
  • Studies of older workers, such as this one, may understate dose-response relations.

Topics

Medical terms in this study, explained in our Lexicon: United States Asbestos Company, Stomach Cancer, Mesothelioma, Asbestos Exposure.

Related studies

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• Cancer mortality in a cohort of asbestos textile workers — E. Pira, C. Pelucchi, et al. (2005)
• Lung and pleural CT signs predict deaths: 10-year follow-up after lung cancer screening of asbestos-exposed workers — T. Vehmas, P. Oksa, et al. (2012)
• Use of death certificates in epidemiological studies, including occupational hazards: variations in discordance of different asbestos-associated diseases on best evidence ascertainment — I.J. Selikoff, H. Seidman (1992)
• Risk of cancer associated with residential exposure to asbestos insulation: a whole-population cohort study — R.J. Korda, M.S. Clements, et al. (2017)

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