Fibrous glass and cancer

Our plain-English summary of Fibrous glass and cancer, by P.F. Infante, L.D. Schuman, J. Dement, et al (American Journal of Industrial Medicine, 1994).

The study

• Authors: P.F. Infante, L.D. Schuman, J. Dement, J. Huff
• Journal: American Journal of Industrial Medicine
• Published: 1994;26(4):559-84
• Type of article: Review
• Cited by: 35 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Some argue that fibrous glass (glass wool) should not be considered as a likely human carcinogen and hence should not be listed in the Seventh Annual Report on Carcinogens (ARC) prepared by the National Toxicology Program (NTP) and mandated by the U.S. Congress. In examining this issue, data from both laboratory experiments (animal studies) and epidemiologic studies (human data) are reviewed with the results evaluated according to the criteria established by the International Agency for Research on Cancer (IARC) and adopted in slightly modified form by the NTP for classifying substances as human carcinogens or likely human carcinogens. From our comprehensive review of the available information, we conclude that fibrous glass materials are carcinogenic, and in view of the NTP and IARC definitions should be listed in the ARC. Our review then examines the carcinogenic potency of glass fibers to humans in comparison with asbestos fibers and concludes that on a fiber-per-fiber basis, glass fibers may be as potent or even more potent than asbestos. The implications of these findings are then presented for regulatory purposes in the occupational setting.

In plain English

This commentary reviewed animal and human evidence on whether fibrous glass (glass wool) should stay listed in the U.S. National Toxicology Program's Annual Report on Carcinogens. An industry petition relied on a negative rat inhalation study by Hesterberg et al. The authors described at least 13 studies in which glass wool injected, implanted or instilled into rats and hamsters raised lung cancer and mesothelioma rates. Eleven inhalation studies were judged inadequate and inconclusive. Reanalyzing the Hesterberg data on male Fischer 344 rats with pooled controls, the authors found a statistically significant dose-response trend for both fiber types combined (p = 0.016). The combined pairwise comparison with controls was not statistically significant (p = 0.094). Their tests used tumor proportions because survival data were not readily available and no survival differences were reported. Reviewed worker studies from Canada, the U.S. and Europe reported raised lung cancer death rates, including a standardized mortality ratio of 199 in Canada. The authors concluded that fibrous glass belongs in the report and that glass fibers may carry lung cancer risk at lower cumulative doses than asbestos.

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: Commentary reviewing published animal experiments and epidemiologic studies of glass wool, with the authors' own statistical reanalysis of one rat inhalation study (Hesterberg et al. 1993) and a risk estimate based on one U.S. worker cohort
• Who was studied: Published animal studies (rats, hamsters, guinea pigs, baboons) and worker cohorts in Canada (Shannon et al., 2,557 men), the U.S. (Enterline et al./Marsh et al., 16,661 male workers at 17 plants) and Europe (Simonato et al., 24,609 workers at 13 factories in seven countries). The reanalysis covered male Fischer 344 rats from the Hesterberg et al. study, with controls pooled from concurrent studies in the same laboratory.
• Exposure: Fibrous glass (glass wool, glass fibers), including the man-made vitreous fibers MMVF 10 and MMVF 11 in the rat inhalation study. Chrysotile, crocidolite and amosite asbestos, and refractory ceramic fibers, appeared as comparison materials. In the animal studies, glass wool was given by intrapleural injection or implantation, intraperitoneal injection, intratracheal instillation and inhalation.
• Main results:
  • In the authors' review of animal studies, at least 13 studies showed increases in lung cancer and mesothelioma in rats and hamsters given glass wool by injection, implantation or instillation. Eleven inhalation studies were reported to find no statistically significant increase, but these were judged inadequate and inconclusive.
  • In the authors' reanalysis of the Hesterberg et al. rat data, pooled controls had a lung tumor incidence of 7/382 (1.8%). Rats exposed to MMVF 11 (all doses, 16/350, 4.6%) had a significantly elevated incidence of lung tumors (p = 0.027). Rats exposed to MMVF 10 (8/354, 2.3%) did not (p = 0.44).
  • With MMVF 10 and MMVF 11 combined (24/704, 3.4%), the pairwise comparison with controls was not statistically significant (p = 0.094).
  • In dose-response trend tests, MMVF 10 showed a statistically significant trend (p = 0.010) and MMVF 11 did not (p = 0.117). The trend for both fiber types combined was statistically significant (p = 0.016).
  • Among the reviewed worker studies, Shannon et al. reported a standardized mortality ratio (SMR) for lung cancer of 199 (19 observed vs 9.53 expected) among Canadian workers producing insulating glass wool.
  • In the reviewed European cohort (Simonato et al.), lung cancer risk more than 20 years after first exposure to glass wool was significant compared with national rates (SMR 139). It was not statistically significant compared with local rates (SMR 111).
  • Using the Marsh et al. U.S. cohort, glass wool workers had a 12% increase in lung cancer relative risk at an average cumulative exposure of 0.4 f/cc-years. Applying an asbestos estimate of roughly a 1% increase per f/cc-year, the authors calculated that the same risk would correspond to roughly 12 f/cc-years if glass wool were as potent as asbestos. They inferred that these synthetic fibers may need a lower cumulative dose than asbestos for the same raised lung cancer risk.
  • Assuming the same potency as asbestos, the authors estimated that an 8-hour time-weighted average exposure of 0.043 f/cc would relate to an excess lung cancer risk of 1 per 1,000 workers over a 45-year working lifetime.
• The authors' conclusion: The authors concluded that the experimental data alone, and the epidemiologic data alone, were each sufficient to list respirable fibrous glass in the Annual Report on Carcinogens. Taken together, in their view, the data place fibrous glass in the category of a likely human carcinogen.
• Limitations the authors state:
  • The reanalysis of the rat data used overall tumor proportions for two reasons: survival data were not readily available, and no survival differences had been reported.
  • The U.S. cohort used for the potency estimate was limited in its detailed exposure information.
  • The authors acknowledged that the potency estimates for synthetic fibers may be higher than the true values. Others had suggested underestimated early exposures or other workplace exposures as possible explanations.

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: IARC, Carcinogenic.

Related studies

• Pathogenicity of a special-purpose glass microfiber (E glass) relative to another glass microfiber and amosite asbestos — R.T. Cullen, A. Searl, et al. (2000)
• Pulmonary response of hamsters to fibrous glass: chronic effects of repeated intratracheal instillation with or without benzo[a]pyrene — V.J. Feron, P.M. Scherrenberg, et al. (1985)
• A comparison of the effects of exposure of baboons to crocidolite and fibrous-glass dusts — B. Goldstein, R.E. Rendall, et al. (1983)
• Chronic inhalation study of fiber glass and amosite asbestos in hamsters: twelve-month preliminary results — T.W. Hesterberg, C. Axten, et al. (1997)
• Tumors of the pleura induced with asbestos and fibrous glass — P. Gross (1973)
• Formation of pseudo-asbestos bodies on sized glass fibres in the hamster lung — A. Holmes, A. Morgan, et al. (1983)

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