Lung cancer mortality and fibre exposures among North Carolina asbestos textile workers

Our plain-English summary of Lung cancer mortality and fibre exposures among North Carolina asbestos textile workers, by D. Loomis, J.M. Dement, S.H. Wolf, et al (Occupational and Environmental Medicine, 2009).

The study

• Authors: D. Loomis, J.M. Dement, S.H. Wolf, D.B. Richardson
• Journal: Occupational and Environmental Medicine
• Published: 2009;66(8):535-42
• Cited by: 98 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To describe mortality among workers exposed to chrysotile asbestos and evaluate the relationship between lung cancer and asbestos fibre exposure.

Methods: Workers employed for at least 1 day between 1 January 1950 and 31 December 1973 in any of four plants in North Carolina, USA that produced asbestos textile products were enumerated. Vital status was ascertained through 31 December 2003. Historical exposures to asbestos fibres were estimated from work histories and 3578 industrial hygiene measurements taken in 1935-1986. Mortality of the cohort was compared with that of the national population via standardised mortality ratios (SMRs). Exposure-response relationships for lung cancer were examined within the cohort using Poisson regression to compute adjusted mortality rate ratios.

Results: Follow-up of 5770 workers included in the cohort resulted in 181 640 person-years of observation, with 2583 deaths from all causes and 277 from lung cancer. Mortality from all causes, all cancers and lung cancer was significant higher than expected, with SMRs of 1.47 for all causes, 1.41 for all cancer and 1.96 (95% CI 1.73 to 2.20) for lung cancer. SMRs for pleural cancer, mesothelioma and pneumoconiosis were also elevated. The risk of lung cancer and asbestosis increased with cumulative fibre exposure (RR 1.102 per 100 fibre-year/ml, 95% CI 1.044 to 1.164, and RR 1.249 per 100 fibre-year/ml, 95% CI 1.186 to 1.316, respectively, for total career exposure).

Conclusions: This study provides further evidence that exposure to chrysotile asbestos in textile manufacturing is associated with increased risk of lung cancer, asbestosis cancer of the pleura and mesothelioma.

In plain English

This retrospective cohort study followed 5,770 people who worked at least one day between 1950 and 1973 at four North Carolina asbestos textile plants, tracing their vital status through 2003. Plant records showed that only chrysotile was used, apart from limited amosite processing at one plant from about 1963 to 1976. Using work histories and air measurements, the authors estimated cumulative fibre exposure for 3,803 workers at three plants. They excluded workers at the fourth plant, workers in non-production jobs and workers with incomplete work histories. Compared with US rates, the workers had more deaths from all causes (standardised mortality ratio, SMR, 1.47), all cancers (SMR 1.41) and lung cancer (SMR 1.96, 95% CI 1.73 to 2.20). Pleural cancer and mesothelioma deaths were also elevated, but each rested on only four deaths. All four mesothelioma deaths were at a plant with no record of amphibole use. Among the 3,803 workers, lung cancer risk rose with cumulative exposure (rate ratio 1.102 per 100 fibre-years/ml, 95% CI 1.044 to 1.164), as did asbestosis risk. The authors concluded that chrysotile exposure in textile manufacturing is associated with increased risk of lung cancer, asbestosis and mesothelioma. Smoking data were inadequate.

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: Retrospective (historical) cohort mortality study. Death rates were compared with national rates using standardised mortality ratios, and exposure-response within the cohort was analysed by Poisson regression.
• Who was studied: 5,770 men and women employed at least 1 day between 1 January 1950 and 31 December 1973 at four asbestos textile plants in North Carolina, USA, followed to 31 December 2003 (181,640 person-years, 2,583 deaths). 3,803 workers were included in the exposure-response analysis.
• Exposure: Chrysotile asbestos in textile manufacturing, plus a limited amount of amosite in a separate operation at plant 3 from about 1963 to 1976. Cumulative fibre exposure (fibre-years/ml) was estimated with a job-exposure matrix built from industrial hygiene samples taken from 1935 to 1986; 3,578 samples were collected in all.
• Main results:
  • Whole cohort compared with the national population: all-cause mortality SMR 1.47 (95% CI 1.41 to 1.53); all-cancer mortality SMR 1.41 (95% CI 1.31 to 1.53).
  • Whole cohort: lung cancer SMR 1.96 (95% CI 1.73 to 2.20), based on 277 lung cancer deaths.
  • Whole cohort: cancer of the pleura SMR 12.43 (95% CI 3.39 to 31.83) and mesothelioma SMR 10.92 (95% CI 2.98 to 27.96). Each was based on only four deaths. Mesothelioma was identified only from 1999 onward.
  • Whole cohort: pneumoconiosis (which includes asbestosis) mortality SMR 3.48 (95% CI 2.73 to 4.38).
  • The lung cancer SMR increased with duration of employment.
  • Exposure-response analysis of 3,803 workers: the lung cancer rate ratio was 1.102 per 100 f-y/ml of total cumulative exposure (95% CI 1.044 to 1.164), adjusted for age, sex, race, calendar decade and birth cohort.
  • Exposure-response analysis of 3,803 workers: the asbestosis rate ratio was 1.258 per 100 f-y/ml of total cumulative exposure (95% CI 1.181 to 1.340) in the full model. A simplified model gave similar results.
  • All four workers whose deaths were coded to mesothelioma had worked at plant 4, where there is no record of amphibole asbestos use.
• The authors' conclusion: The authors concluded that the study provides further evidence that chrysotile exposure in asbestos textile manufacturing is associated with increased risk of lung cancer, asbestosis and mesothelioma. They added that further work is needed to reconcile their exposure-response slopes with those from other textile cohorts.
• Limitations the authors state:
  • Smoking information was inadequate, so smoking could not be adjusted for and the smoking-asbestos interaction could not be assessed.
  • Exposure could not be estimated for some workers because industrial hygiene data were lacking for one of the four plants and for non-production jobs. These workers, and workers with missing work history data, were excluded.
  • These exclusions reduced the precision of the exposure-response estimates.
  • Job data were missing for about a quarter of the cohort, which may have reduced exposure contrasts and weakened the associations.
  • Mesothelioma was likely under-reported in the early years of the study, so cases before 1999 may have been missed.
  • There were too few pleural cancer and mesothelioma deaths for exposure-response analysis of those outcomes.
  • Exposure data and work histories were of lower quality than in the South Carolina cohort, so exposure estimates may be more uncertain and associations more attenuated.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Chrysotile, Industrial Hygiene, rate ratio, Mesothelioma, Pneumoconiosis, Pleura.

Related studies

• Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers — L. Elliott, D. Loomis, et al. (2012)
• Estimates of historical exposures by phase contrast and transmission electron microscopy for pooled exposure--response analyses of North Carolina and South Carolina, USA asbestos textile cohorts — J.M. Dement, D. Loomis, et al. (2011)
• Estimates of historical exposures by phase contrast and transmission electron microscopy in North Carolina USA asbestos textile plants — J.M. Dement, D. Myers, et al. (2009)
• Increased lung cancer mortality among chrysotile asbestos textile workers is more strongly associated with exposure to long thin fibres — D. Loomis, J.M. Dement, et al. (2012)
• Mortality among North Carolina construction workers, 1988-1994 — E. Wang, J.M. Dement, et al. (1999)
• Cancer and noncancer mortality among aluminum smelting workers in Badin, North Carolina — E.S. McClure, P. Vasudevan, et al. (2020)

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