A 30-year mortality and respiratory morbidity study of refractory ceramic fiber workers

Our plain-English summary of A 30-year mortality and respiratory morbidity study of refractory ceramic fiber workers, by G. LeMasters, J.E. Lockey, T.J. Hilbert, et al (Inhalation Toxicology, 2017).

The study

• Authors: G. LeMasters, J.E. Lockey, T.J. Hilbert, L.S. Levin, J.W. Burkle, R. Shipley, C. Perme, C.A. Meyer, C.H. Rice
• Journal: Inhalation Toxicology
• Published: 2017;29(10):462-470
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Aim: Report mortality (n = 1119), cancer incidence (n = 1207) and radiographic (n = 1451) findings from a 30-year investigation of current and former refractory ceramic fiber (RCF) workers.

Methods: Cause of death, health and work histories, radiographs and spirometry were collected. Mortality and cancer incidence were analyzed. Logistic regression analysis investigated the associations of latency and cumulative fiber exposure (CFE) on radiographic changes.

Results: The mortality study showed no increase in standardized mortality rates (SMR) for lung cancer, but urinary cancers were significantly elevated in the higher exposed group (SMR = 3.62, 95% CI: 1.33-7.88) and leukemia in the total cohort (SMR = 2.51, 95% CI: 1.08-4.94). One death attributed to mesothelioma was identified (SMR = 2.86, 95% CI: 0.07-15.93) in a worker reporting some asbestos exposure. The overall rate of pleural changes was 6.1%, attaining 21.4% in the highest CFE category for all subjects (adjusted odds ratio (aOR) = 6.9, 95% CI: 3.6-13.4), and 13.0% for those with no reported asbestos exposure (OR= 9.1, 95% CI: 2.5-33.6). Prevalence for recent hires (≥1985) was similar to the background. Interstitial changes were not elevated. Localized pleural thickening was associated with small decreases in spirometry results.

Conclusion: Increases in leukemia and urinary cancer but not lung cancer mortality were found. One death attributed to mesothelioma was observed in a worker with self-reported asbestos exposure and a work history where occupational asbestos exposure may have occurred, rendering uncertainties in assigning causation. Radiographic analyses indicated RCF exposure alone is associated with increased pleural but not interstitial changes. Reductions in RCF exposure should continue. The mortality study is ongoing.

In plain English

This 30-year cohort study followed workers making refractory ceramic fiber (RCF), a synthetic fiber, at five U.S. plants. The mortality analysis covered 1,119 New York and Indiana workers followed through 2015; 234 died. Lung cancer deaths were not increased. Urinary organ cancer deaths were raised among workers with more than 45 fiber-months/cc of cumulative exposure (6 deaths; SMR 3.62, 95% CI 1.33–7.88). Leukemia deaths were raised in the whole group (8 deaths; SMR 2.51, 95% CI 1.08–4.94). One death was attributed to mesothelioma (type unspecified) in a worker reporting some asbestos exposure. This was not statistically significant, and medical records could not be obtained to confirm it. Of 1,451 workers X-rayed, 6.1% had pleural changes, rising to 21.4% at the highest exposure. No statistically significant association was found between interstitial changes and cumulative exposure or time since hire. The authors concluded that RCF was associated with pleural changes in an exposure-response pattern and that continued exposure reduction is prudent. They judged the leukemia finding unlikely to relate to RCF; their incidence survey did not support the urinary cancer finding.

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: Longitudinal cohort study (30-year follow-up) combining a mortality study, a questionnaire-based cancer incidence study, and repeated chest radiographs and spirometry
• Who was studied: Current and former RCF manufacturing workers at five U.S. facilities: Western New York (45%), Indiana (18%), Georgia (20%), Tennessee (11%) and Oklahoma (6%). Enrollment ran from 1987 to 1999. The mortality study included 1,119 workers hired from 1952 through 1999 at the New York (818) and Indiana (301) plants, followed to 31 December 2015. The cancer incidence study included 1,207 workers. The radiographic study included 1,451 workers with radiographs taken from 1987 to 2014.
• Exposure: Refractory ceramic fiber, measured as estimated cumulative fiber exposure (fiber-months/cc). The highest estimated exposure was 10 fibers/cc, for carding in the 1950s. No routine asbestos use was identified at the plants. About half the workers (762) reported some asbestos exposure, with a median duration of 3 months. Some workers also had minor exposure to alkaline earth silicate wools or polycrystalline wool.
• Main results:
  • Whole mortality cohort (1,119): 234 deaths. Deaths from all causes were lower than expected (SMR 0.73, 95% CI 0.64–0.83). Lung cancer deaths (trachea, bronchus, lung) were not increased (23 deaths; SMR 0.83, 95% CI 0.53–1.25).
  • Workers with more than 45 fiber-months/cc cumulative exposure (285): urinary organ cancer deaths were significantly elevated (6 deaths; SMR 3.62, 95% CI 1.33–7.88). In the whole cohort the urinary organ cancer SMR was 1.80 (8 deaths; 95% CI 0.78–3.55).
  • Whole cohort: leukemia deaths were significantly elevated (8 deaths; SMR 2.51, 95% CI 1.08–4.94). The elevation was not significant in the higher-exposed group (3 deaths; SMR 2.57, 95% CI 0.53–7.50).
  • One death was attributed to mesothelioma, unspecified (ICD-10 C45.9). The SMR was not statistically significant (2.86, 95% CI 0.07–15.93 in the whole cohort; 7.85, 95% CI 0.20–43.76 in the higher-exposed group). This worker reported asbestos exposure, including work as an auto mechanic changing clutch plates and brakes.
  • Cancer incidence (self-reported by questionnaire since 2003): 4 respiratory cancers were reported against 9.9 expected (SIR 0.40), and 2 urinary cancers against 6.4 expected (SIR 0.31). No mesothelioma cases were identified this way.
  • Pleural changes were seen in 6.1% of all 1,451 workers (89), 9.0% of former workers and 4.1% of those with no reported asbestos exposure.
  • Pleural changes rose with cumulative exposure. All subjects: 9.1% at more than 45–135 fiber-months/cc (aOR 2.6, 95% CI 1.4–4.6) and 21.4% (22 of 103) above 135 fiber-months/cc (aOR 6.9, 95% CI 3.6–13.4).
  • Workers with no reported asbestos exposure: odds ratios were significant in the two highest exposure groups. These were OR 5.7 (95% CI 1.8–17.6) at more than 45–135 fiber-months/cc and OR 9.1 (95% CI 2.5–33.6) above 135 fiber-months/cc, where 6 of 46 (13.0%) had pleural changes.
  • Recent hires (n = 511): 5 workers (1.0%) had localized pleural thickening and 3 (0.6%) had interstitial changes. The authors described this as similar to background rates.
  • Interstitial changes were seen in 22 of 1,450 workers (1.5%). No significant association was identified with latency or cumulative exposure after adjusting for pack-years and age. In the highest exposure group (above 135 fiber-months/cc), 3 of 104 (2.9%) had them (aOR 1.2, 95% CI 0.3–5.9).
  • Localized pleural thickening (plaques) alone was associated with a small decrease in percent predicted FVC and, to a lesser extent, FEV1, compared with normal radiographs. The table notes that these estimated changes were not statistically significant.
• The authors' conclusion: The authors concluded that after 30 years there was no excess of lung cancer deaths and no significant association with interstitial fibrosis on radiographs. They judged the single mesothelioma death uncertain, because the worker had some reported asbestos exposure, possible unreported exposure, and an unconfirmed diagnosis. They found that pleural changes were associated with RCF in an exposure-response relationship, so continued reduction of RCF exposure is prudent in manufacturing and end-user settings. They noted that the incidence study did not support the urinary cancer mortality finding, and judged the leukemia increase unlikely to be related to RCF. The mortality study will continue.
• Limitations the authors state:
  • Pleural changes were assessed with chest radiographs rather than CT, which is better at detecting them.
  • The workers were still relatively young (mean age 63.1), while the average age at lung cancer diagnosis is 70, so the absence of excess lung cancer is cautionary.
  • Exposure levels at the study plants may differ from other manufacturing facilities or end-users, limiting generalizability.
  • Medical records were unavailable for the incidence and mortality studies, so the leukemia and urinary cancer findings should be interpreted with caution.
  • The mesothelioma diagnosis could not be confirmed, because attempts to retrieve medical records failed.
  • Self-reported incident cancers were not verified with medical records and were used only for qualitative comparisons.
  • The sample with pleural plaques in the lung function analysis was small, and the long-term biologic implications are unknown.

Topics

Medical terms in this study, explained in our Lexicon: Spirometry, Latency, Lung Cancer, Mesothelioma, Asbestos Exposure, Odds Ratio, Interstitial, Pleural Thickening.

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)
• Perspectives on refractory ceramic fiber (RCF) carcinogenicity: comparisons with other fibers — H. Greim, M.J. Utell, et al. (2014)
• Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers — A.M. Walker, L.D. Maxim, et al. (2002)
• Pulmonary and pleural leukocytes from F344 rats produce elevated levels of fibronectin following inhalation of refractory ceramic fibers — T.R. Gelzleichter, J.B. Mangum, et al. (1996)
• Refractory ceramic fiber (RCF) toxicity and epidemiology: a review — M.J. Utell, L.D. Maxim (2010)
• Refractory ceramic fiber exposure and pleural plaques — J. Lockey, G. Lemasters, et al. (1996)

Browse more research in Inhalation Toxicology, or return to medical research.