Cause-specific mortality in relation to chrysotile-asbestos exposure in a Chinese cohort

Our plain-English summary of Cause-specific mortality in relation to chrysotile-asbestos exposure in a Chinese cohort, by S. Lin, X. Wang, I.T. Yu, et al (Journal of Thoracic Oncology, 2012).

The study

• Authors: S. Lin, X. Wang, I.T. Yu, E. Yano, M. Courtice, H. Qiu, M. Wang
• Journal: Journal of Thoracic Oncology
• Published: 2012;7(7):1109-14
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: The carcinogenic potency of chrysotile asbestos remains a contentious topic, and more data are needed to address this issue. We examine cause-specific mortality, especially lung cancer, and its association with chrysotile-asbestos exposure in a Chinese cohort.

Methods: A cohort of 577 workers from a chrysotile-textile plant was followed prospectively from 1972 to 2008. Occupational history, exposure information, and smoking data were obtained from company records and personal interviews; vital status and causes of death were ascertained from death registries and hospitals. Workers were classified into three exposure levels on the basis of exposure assessments of different workshops. Standardized Mortality Ratios (SMRs) were calculated in terms of exposure levels and other indices.

Results: Among 259 identified deaths, 53 died from lung cancer, with an SMR of 4.08 (95% confidence interval 3.12, 5.33), and 96 from all cancers with an SMR of 2.09 (1.71, 2.55). In addition, two deaths from mesothelioma were observed. Increased mortality from respiratory diseases was also observed (SMR 3.38, 95% confidence interval 2.72, 4.21). Asbestos-exposure levels, exposure years, and birth cohorts showed a clear trend of risk for lung cancer and respiratory diseases.

Conclusion: The current analysis indicated that exposure to chrysotile asbestos was closely associated with excess mortality from lung cancer and respiratory diseases.

In plain English

This prospective cohort study compared deaths among male workers at a Chinese chrysotile asbestos plant with Chinese national male rates. Of 586 workers enrolled in 1972, nine were lost and 259 died by 2008. Lung cancer caused 53 deaths against 13.0 expected (standardized mortality ratio, SMR, 4.08; 95% CI 3.12 to 5.33). All cancers caused 96 deaths against 46.0 expected (SMR 2.09; 95% CI 1.71 to 2.55). Nonmalignant respiratory diseases caused 81 deaths (SMR 3.38; 95% CI 2.72 to 4.21), 39 diagnosed as asbestosis. Two workers died of mesothelioma (one pleural, one peritoneal). The lung cancer SMR rose from 2.21 (95% CI 1.36 to 3.59) at low exposure to 7.69 (5.29 to 11.19) at high exposure. It was also higher with longer exposure, first exposure before age 25, and earlier birth. Gastrointestinal cancer deaths were slightly above expected (SMR 1.31; 95% CI 0.91 to 1.89); the authors said asbestos might not explain this. The authors concluded that excess mortality from lung cancer, all cancers and nonmalignant respiratory diseases was associated with chrysotile exposure. They noted that exposure was estimated from jobs and nonsmokers were few.

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: Prospective cohort study (updated analysis) using standardized mortality ratios against Chinese national male mortality rates
• Who was studied: 586 active male workers at a chrysotile-asbestos manufacturing plant in China, enrolled January 1, 1972 and followed to December 31, 2008; 9 were lost to follow-up, leaving 577
• Exposure: Relatively pure chrysotile asbestos, from two local Sichuan mines before the 1990s and partly imported from Russia and Canada since 1998. It was used for textiles, friction and heat-resistant materials, cement and rubber products. In 2002 the median fiber concentration was 7.2 f/ml in the raw-material workshop, 2.1 f/ml in textile workshops and 0.8 f/ml in the rubber section. Workers were grouped as high exposure (raw-material and textile), medium (maintenance) or low (rubber, cement, administration, other services).
• Main results:
  • Whole cohort, all causes: 259 deaths observed versus 197.3 expected (SMR 1.31; 95% CI 1.16, 1.48)
  • Whole cohort, lung cancer: 53 deaths versus 13.0 expected (SMR 4.08; 95% CI 3.12, 5.33)
  • Whole cohort, all cancers: 96 deaths versus 46 expected (SMR 2.09; 95% CI 1.71, 2.55)
  • Whole cohort, gastrointestinal cancers: 29 deaths versus 22.1 expected (SMR 1.31; 95% CI 0.91, 1.89). The authors described this as slightly higher than expected.
  • Gastrointestinal cancer SMRs by exposure level (1.61 low, 0.89 medium, 1.04 high) showed no clear trend. The authors said the slight excess might not result from asbestos exposure but from other confounding factors such as diet.
  • Two mesothelioma deaths, one pleural and one peritoneal. One worker was from the raw-materials workshop with 14 years of exposure; the other was from the weaving workshop with 33 years of exposure.
  • Whole cohort, nonmalignant respiratory diseases (all such deaths combined): 81 deaths (SMR 3.38; 95% CI 2.72, 4.21); 39 of these deaths were diagnosed as asbestosis
  • Lung cancer SMR by exposure level: low 2.21 (95% CI 1.36, 3.59), medium 4.46 (2.42, 8.22), high 7.69 (5.29, 11.19); p for trend less than 0.001
  • Lung cancer was higher in smokers than nonsmokers at each exposure level except the high level. High-exposure nonsmokers had an SMR of 7.02 (95% CI 2.73, 18.05; 4 deaths), compared with 7.80 for high-exposure smokers. Low-exposure nonsmokers had an SMR of 0.53 (0.09, 3.03; 1 death).
  • Lung cancer SMR was 6.45 (95% CI 4.18, 9.97) in workers with 15 or more years of exposure at entry, and 5.24 (3.58, 7.68) in workers with 25 or more total exposure years
  • Lung cancer SMR was 7.08 (95% CI 4.36, 11.50) in workers first exposed before age 25, compared with 3.64 (age 25 to 34) and 3.26 (age 35 or older)
  • Lung cancer SMR was 6.98 (95% CI 3.20, 15.22) in workers born before 1925, 5.22 for those born 1925 to 1940, and 3.10 for those born after 1940. It was 7.21 (4.37, 11.90) for workers aged 50 or older at entry.
• The authors' conclusion: The authors concluded that the cohort had significantly increased mortality from lung cancer, all cancers and nonmalignant respiratory diseases relative to Chinese national rates. They found this increase associated with chrysotile exposure level, exposure years, age at first exposure and birth period.
• Limitations the authors state:
  • There was no complete individual fiber-exposure data, so job titles and workshops were used as a surrogate. Misclassification of exposure was likely and could weaken the exposure-response gradient.
  • The small number of nonsmoking workers made results unstable, with wide confidence intervals when stratified by exposure level
  • Reference rates came from nationwide mortality surveys from different periods because the national cancer registry was incomplete, especially before 1981
  • Lung cancer SMRs for nonsmokers may have been underestimated, because the national reference rates included both smokers and nonsmokers

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Asbestos Exposure, Carcinogenic, Lung Cancer, Occupational History, standardized mortality ratio (SMR), confidence interval, Mesothelioma.

Related studies

• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)
• Mortality in a Chinese chrysotile miner cohort — X. Wang, S. Lin, et al. (2012)
• Cancer mortality in Chinese chrysotile asbestos miners: exposure-response relationships — X. Wang, E. Yano, et al. (2013)
• Cancer mortality among Chinese chrysotile asbestos textile workers — X.R. Wang, I.T. Yu, et al. (2012)
• Exposure-response estimate for lung cancer and asbestosis in a predominantly chrysotile-exposed Chinese factory cohort — M.N. Courtice, X. Wang, et al. (2016)
• Exposure to chrysotile mining dust and digestive cancer mortality in a Chinese miner/miller cohort — S. Lin, X. Wang, et al. (2014)

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