Mortality of brain tumors among asbestos insulation workers in the United States and Canada

Our plain-English summary of Mortality of brain tumors among asbestos insulation workers in the United States and Canada, by H. Seidman, I.J. Selikoff, E.C. Hammond (Annals of the New York Academy of Sciences, 1982).

The study

• Authors: H. Seidman, I.J. Selikoff, E.C. Hammond
• Journal: Annals of the New York Academy of Sciences
• Published: 1982;381:160-71
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001764).

Abstract

Death resulting from brain tumors among workers in the petrochemical industry have called attention to the possibility that these neoplasms may be the result of occupational exposure to carcinogens. We have examined the experience of a cohort of 17,800 insulation workers known to be at significant increased risk of cancer at a number of sites (lung, mesothelioma, gastrointestinal, oral cavity, pharyngeal, larynx, renal) to ascertain whether their asbestos exposure also increased their risk of brain tumors. From 1967 to 1979, there were 24 deaths from primary brain tumors in this cohort, somewhat more than were anticipated (18.0 such deaths were expected based on U.S. general population data, and 20.5 if smoking was taken into account). The excess was not "statistically significant" at the 5% level although this does not rule out the possibility of an etiological association. It was of interest that the observed excess was concentrated (about twice expected) among insulators in the younger ages (those under 50) and during the early period after onset of work (15-24 years), in contrast with age distribution and latency in other asbestos-associated neoplasms. This may have relevance to theoretical concerns about questions of initiation and promotion in the etiology of cancer, particularly with regard to brain tumors.

In plain English

This prospective cohort study followed 17,800 men on the rolls of the asbestos insulation workers' union in the United States and Canada on January 1, 1967, recording deaths through December 31, 1979. The men mainly did construction insulation work with products containing chrysotile and, from the mid-1930s, amosite. Causes of death were assigned from death certificates and from 'best evidence', including autopsy and surgical material. By best evidence, 24 men died of primary brain tumors (26 by death certificates). That compared with 18.0 deaths expected from U.S. general population rates, and 20.5 when smoking was taken into account. This excess was not statistically significant at the 5% level; the authors said this does not rule out an association. The excess was concentrated in men under 50, at about twice expected. It was also concentrated at 15 to 24 years after starting work (12 observed, 5.6 expected), unlike other asbestos-related cancers. Smoking showed little relationship to brain tumors. The authors noted the data were sparse. They suggested the pattern may bear on theories of cancer initiation and promotion.

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
• Who was studied: 17,800 men on the rolls of the asbestos insulation workers' union in the United States and Canada on January 1, 1967, followed from January 1, 1967 to December 31, 1979. They were mainly building-trades construction insulators; a few worked in petrochemical settings. 'Brain' tumors here include brain, eye and other parts of the nervous system.
• Exposure: Asbestos insulation work, described as limited, varied and intermittent. Chrysotile alone was used until about the early 1940s. Amosite was used from the mid-1930s in small quantities, and more widely from World War II. Magnesia block insulation contained about 15% asbestos. The authors estimated time-weighted average dust levels, printed as '4-1 2 fibers/ml', apparently 4 to 12 fibers/ml.
• Main results:
  • Whole cohort, 1967-1979: 24 deaths from primary brain tumors by best evidence. Expected deaths were 18.0 from U.S. general population rates, or 20.5 when smoking was taken into account.
  • The excess was not statistically significant at the 5% level. The authors said this does not rule out an etiological association.
  • Men under age 50: brain tumor deaths were about twice expectation (under 40: 5 observed versus 2.4 expected; 40-49: 8 observed versus 4.4 expected). Older age groups were close to expected (50-59: 5 versus 5.2; 60 and over: 6 versus 6.0).
  • By time since starting asbestos work, brain tumor mortality ratios peaked at 15-24 years (12 observed versus 5.6 expected). This is earlier than the peak for lung cancer in this cohort. The highest risk was at 15-24 years after onset among workers under 50, though the data were sparse.
  • Cigarette smoking showed little relationship to brain tumor deaths among the insulators.
  • Death certificates listed 26 brain tumor deaths and best evidence listed 24, with agreement on 23 cases. Tissue verification (9 autopsies, 16 surgical specimens) was lacking in only 2 instances.
  • Assuming the excess is real, brain tumors accounted for about 1% of the excess mortality observed in the cohort (1967-1976 data).
• The authors' conclusion: The authors concluded that whatever excess there may be is concentrated in men under 50 and at 15 to 24 years after onset of work. This may have relevance to theoretical questions of initiation and promotion in carcinogenesis, but the authors said it seems quite obscure otherwise.
• Limitations the authors state:
  • The data cross-tabulating years since onset of work by age are quite sparse.
  • Few dust measurements were made in insulation work before the mid-1960s, so exposure levels were estimated by reconstruction and extrapolation.

Topics

Medical terms in this study, explained in our Lexicon: Insulator, Neoplasm, Occupational Exposure, Mesothelioma, Asbestos Exposure, Latency, Etiology.

Related studies

• Mortality experience of insulation workers in the United States and Canada, 1943--1976 — I.J. Selikoff, E.C. Hammond, et al. (1979)
• Asbestos-associated deaths among insulation workers in the United States and Canada, 1967-1987 — I.J. Selikoff, H. Seidman (1991)
• The investigation of brain tumor occurrence in other occupational groups: introduction — I.J. Selikoff (1982)
• Occupational risk factors for brain cancer in Canada — S.Y. Pan, A.M. Ugnat, et al. (2005)
• The occurrence of asbestosis among insulation workers in the United States — I.J. Selikoff, J. Churg, et al. (1965)
• Neoplasia among insulation workers in the United States with special reference to intra-abdominal neoplasia — E.C. Hammond, I.J. Selikoff, et al. (1965)

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