Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers

Our plain-English summary of Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers, by A.M. Walker, L.D. Maxim, M. Utell (Regulatory Toxicology and Pharmacology, 2002).

The study

• Authors: A.M. Walker, L.D. Maxim, M. Utell
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2002;35(1):95-104
• Type of article: Review
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Although workers in refractory ceramic fibers (RCF) manufacturing facilities have experienced no elevations in lung cancer or mesothelioma rates, the historical experience of asbestos together with animal studies of RCF have led to ongoing studies of the respiratory health of RCF workers. We have compared lung cancer and mesothelioma in the accumulated mortality experience of a cohort of male RCF production workers (Lemasters et al., 2001, submitted for publication) to that which would have been expected if RCF had a carcinogenic potency similar to that of various forms of asbestos. To accomplish this, we used risk models recently formalized by Hodgson and Darnton (2000, Ann. Occup. Hyg. 41, 13-36) for asbestos cohorts together with the RCF exposure measurements and historical reconstructions of Rice and colleagues (1997, Appl. Occup. Environ. Hyg. 12, 54-61). Deaths from lung cancer in the RCF cohort are statistically significantly below that which would be expected if RCF had the potency of either crocidolite or amosite. The mortality is also lower than would be expected if RCF had the potency of chrysotile, but the difference is not statistically significant. For mesothelioma, the anticipated numbers of deaths under hypotheses of asbestos-like potency are too small to be rejected by the zero cases seen in the RCF cohorts. The current epidemiologic studies do not rule out risk, but they clearly do rule out lung cancer risks like those of crocidolite or amosite. The residual uncertainty justifies ongoing workplace surveillance.

© 2002 Elsevier Science (USA).

In plain English

The authors used data from an ongoing University of Cincinnati study of male refractory ceramic fiber (RCF) workers, analyzing men in production jobs. They applied mathematical models published by Hodgson and Darnton for asbestos-exposed workers to estimate how many lung cancer and mesothelioma deaths would have been expected if RCF were as potent as crocidolite, amosite or chrysotile asbestos. The cohort had 6 lung cancer deaths against 9.35 expected from U.S. rates for men, a standardized mortality ratio (SMR) of 64 (upper 95% confidence bound 127). A potency like that estimated for crocidolite or amosite was statistically rejected (P = 0.04). For chrysotile-like potency, the difference was not statistically significant (P = 0.17). No mesothelioma deaths occurred. However, the expected numbers under asbestos-like potency were so small (crocidolite 1.61, amosite 0.32, chrysotile 0.02) that zero cases could not reject asbestos-like risk. The authors concluded the data do not rule out risk but do rule out lung cancer risks like those of crocidolite or amosite. They noted the cohort was still relatively young, and that exposures before 1987 were reconstructed from plant engineering histories and a few historical measurements and may contain significant inaccuracies.

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: Risk analysis: mathematical asbestos risk models applied to the mortality data of an existing cohort of RCF workers, comparing observed deaths with deaths anticipated under hypotheses of asbestos-like potency
• Who was studied: University of Cincinnati cohort of male RCF workers with at least 1 year of employment at one of two plants, hired on or before December 31, 1997 (927 workers, production and nonproduction, earliest hire August 1, 1952). This analysis used data for the men in production jobs.
• Exposure: Refractory ceramic fibers (man-made vitreous fibers for high-temperature insulation). Estimated exposures ranged from about 10 fibers/cc (8-hour time-weighted average) in the 1950s for carding in a textile operation to well below 1 fiber/cc in most jobs in the 1990s. Cumulative exposure in the cohort averaged somewhat less than 1 fiber/cc year.
• Main results:
  • In the RCF cohort, 6 deaths from trachea, bronchus and lung cancer occurred (all lung), against 9.35 expected from U.S. rates for men in the general population
  • Lung cancer SMR in the RCF cohort was 64 (upper 95% confidence bound 127)
  • The upper 95% confidence bound for the RCF cohort corresponded to a lung cancer potency (RL) of 4.25% increase per fiber/cc year
  • Under the Hodgson and Darnton lung cancer potency for crocidolite or amosite (5.0% per fiber/cc year), 12.30 deaths would have been anticipated. This hypothesis was rejected for RCF (P = 0.04, likelihood ratio 0.27).
  • Under chrysotile-like lung cancer potency (0.1%), anticipated deaths (9.41) were very close to the no-effect level. This was not statistically distinguishable (P = 0.17, likelihood ratio 0.98).
  • No mesothelioma deaths occurred among RCF workers
  • Anticipated mesothelioma deaths under asbestos-like potency were 1.61 for crocidolite, 0.32 for amosite and 0.02 for chrysotile. These were too small for zero observed cases to reject asbestos-like risk; the probability of no deaths under crocidolite-like potency was 0.20.
  • The upper 95% confidence bound for mesothelioma potency (RM) in the RCF cohort was 27.9 × 10−8, nearly as high as the highest crocidolite value in the asbestos cohorts
• The authors' conclusion: The authors concluded that the current epidemiologic studies do not rule out risk, but do rule out lung cancer risks like those of crocidolite or amosite
• Limitations the authors state:
  • The cohort is still relatively young
  • Exposures before 1987 were reconstructed from plant engineering histories and a few historical measurements and may contain significant inaccuracies
  • The comparison with the lowest (chrysotile-range) asbestos lung cancer potency estimates has little statistical power
  • It is too early to make any definitive statement about mesothelioma

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Mesothelioma, Carcinogenic, Crocidolite, Amosite, Chrysotile.

Related studies

• Biopersistence of refractory ceramic fiber in human lung tissue and a 20-year follow-up of radiographic pleural changes in workers — J.E. Lockey, V.L. Roggli, et al. (2012)
• A 30-year mortality and respiratory morbidity study of refractory ceramic fiber workers — G. LeMasters, J.E. Lockey, et al. (2017)
• Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity? — A.M. Walker, L.D. Maxim, et al. (2012)
• Refractory ceramic fiber (RCF) toxicity and epidemiology: a review — M.J. Utell, L.D. Maxim (2010)
• Perspectives on refractory ceramic fiber (RCF) carcinogenicity: comparisons with other fibers — H. Greim, M.J. Utell, et al. (2014)
• Refractory ceramic fibers: Fiber characteristics, potential health effects and clinical observations — M.J. Utell, L.D. Maxim (2018)

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