Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity?

Our plain-English summary of Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity?, by A.M. Walker, L.D. Maxim, M.J. Utell (Inhalation Toxicology, 2012).

The study

• Authors: A.M. Walker, L.D. Maxim, M.J. Utell
• Journal: Inhalation Toxicology
• Published: 2012;24(7):416-24
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Animal studies on refractory ceramic fiber (RCF) have led to the suggestion that RCF might resemble asbestos in carcinogenicity. Human data are available to test this hypothesis.

Methods: We compared the occurrence of lung cancer and mesothelioma in 605 men engaged in the manufacture of RCF and followed since 1987 to cancer rates that would have been anticipated if airborne RCF were carcinogenic to the same degree as are crocidolite, amosite or chrysotile asbestos. We integrated the results of workplace exposure monitoring with mortality follow-up using formulas presented by Hodgson and Darnton (2000) to estimate hypothesized risks under different asbestos scenarios.

Results: During 15,281 person-years of observation, there were 12 deaths from lung cancer. General population rates predicted 11.8 cases expected for an observed/expected (O/E) ratio of 1.0. Anticipated numbers of deaths from lung cancer under hypotheses of carcinogenicity similar to that of amphiboles and chrysotile were 62 and 17, allowing for rejection of amphibole-like effects (p < 10(-5)) but not chrysotile-like carcinogenicity (p = 0.15). There were no cases of mesothelioma, as compared to 4.9 anticipated under a crocidolite-like hypothesis (p = 0.007 to reject), 1.0 for amosite (p = 0.38) and 0.05 for chrysotile (p = 0.95).

Conclusion: There was no increase in lung cancer or mesothelioma in these workers exposed to RCF. If the cohort had the same exposure to crocidolite asbestos the number of lung cancer and mesothelioma cases would have been significantly greater than observed. The data do not yet permit a similar conclusion with respect to chrysotile asbestos.

In plain English

This study followed 605 men in production jobs at US refractory ceramic fiber (RCF) plants, counting lung cancer and mesothelioma deaths from 1970 to 2008. The authors compared lung cancer deaths with the numbers expected from US male lung cancer death rates. They also compared lung cancer and mesothelioma deaths with the numbers anticipated if airborne RCF caused cancer as strongly as crocidolite, amosite or chrysotile asbestos, given each worker's estimated cumulative RCF exposure. There were 12 lung cancer deaths, against 11.8 expected. If RCF had acted like amphibole asbestos, 61.6 lung cancer deaths would have been anticipated (p less than 0.00001). If it had acted like chrysotile, 16.8 would have been anticipated (p = 0.15); this could not be rejected. There were no mesothelioma deaths. Only a crocidolite-like effect, with 4.90 cases anticipated, was rejected (p = 0.007). Amosite-like effects (0.98 anticipated) and chrysotile-like effects (0.05 anticipated) were not rejected. The authors concluded there was no increase in lung cancer or mesothelioma in these workers, but that the data cannot yet rule out RCF being as carcinogenic as chrysotile.

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 analysis. Observed lung cancer deaths were compared with deaths expected from general-population rates. Observed lung cancer and mesothelioma deaths were compared with deaths anticipated under asbestos-potency scenarios, using the Hodgson and Darnton (2000) formulas.
• Who was studied: 605 male production workers at US refractory ceramic fiber plants, observed 1970–2008 while aged 25 and older (15,281 person-years)
• Exposure: Estimated cumulative exposure to airborne refractory ceramic fiber, grouped as 0–15, 15–45, 45–135 and 135 or more fiber-months per cubic centimeter. Asbestos exposure was not measured; the asbestos comparisons were calculated hypothetical scenarios.
• Main results:
  • In the whole cohort there were 12 lung cancer deaths, against 11.8 expected from US male general population rates (observed/expected ratio 1.0).
  • The 12 observed lung cancer deaths were far fewer than the 61.6 anticipated if RCF were as carcinogenic as amphibole asbestos (p less than 0.00001).
  • The 12 observed lung cancer deaths were statistically compatible with the 16.8 anticipated under a chrysotile-like effect (p = 0.15). They were also compatible with no asbestos-like effect (p = 0.60).
  • There was no association between lung cancer risk trends and cumulative RCF exposure or calendar year.
  • There were no mesothelioma deaths.
  • Against zero observed mesothelioma deaths, only the crocidolite-like scenario (4.90 anticipated) was rejected (p = 0.007). The amosite-like scenario (0.98 anticipated, p = 0.376) and the chrysotile-like scenario (0.05 anticipated, p = 0.952) were not rejected (Table 4).
• The authors' conclusion: The authors concluded that there was no increase in lung cancer or mesothelioma in these RCF-exposed workers. They also concluded that, had the cohort had the same exposure to crocidolite, lung cancer and mesothelioma cases would have been significantly greater than observed.
• Limitations the authors state:
  • The data did not allow the authors to rule out RCF being as potent as chrysotile asbestos for lung cancer or mesothelioma.
  • Under the Hodgson and Darnton formulas, the effects of chrysotile were scarcely distinguishable from the no-effect level, even with the extended follow-up.
  • Office and research-and-development jobs were excluded, even though some of these jobs involved RCF exposure that was not well characterized.

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, Amphibole Group.

Related studies

• Perspectives on refractory ceramic fiber (RCF) carcinogenicity: comparisons with other fibers — H. Greim, M.J. Utell, et al. (2014)
• Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry — T.J. Lentz, C.H. Rice, et al. (1999)
• Corrigendum. Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity? — A.M. Walker, L.D. Maxim, et al. (2012)
• Refractory ceramic fibers: Fiber characteristics, potential health effects and clinical observations — M.J. Utell, L.D. Maxim (2018)
• Refractory ceramic fiber (RCF) toxicity and epidemiology: a review — M.J. Utell, L.D. Maxim (2010)
• Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers — A.M. Walker, L.D. Maxim, et al. (2002)

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