Exposure-response estimate for lung cancer and asbestosis in a predominantly chrysotile-exposed Chinese factory cohort

Our plain-English summary of Exposure-response estimate for lung cancer and asbestosis in a predominantly chrysotile-exposed Chinese factory cohort, by M.N. Courtice, X. Wang, S. Lin, et al (American Journal of Industrial Medicine, 2016).

The study

• Authors: M.N. Courtice, X. Wang, S. Lin, I.T. Yu, D.W. Berman, E. Yano
• Journal: American Journal of Industrial Medicine
• Published: 2016;59(5):369-78
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Cumulative fiber exposures, predominantly chrysotile, were estimated in a Chinese asbestos worker cohort and exposure-response relationships with lung cancer mortality and cumulative incidence of asbestosis were determined.

Methods: Individual time-dependent cumulative exposures were estimated for 577 asbestos workers, followed prospectively for 37 years. Occupational history and smoking data were obtained from company records and personal interviews; vital status and causes of death were ascertained from death registries and hospital records. Hazard ratios were generated for disease outcomes, with adjustments for smoking and age.

Results: Median cumulative fiber exposure for the cohort was 132.6 fiber-years/ml (IQR 89.3-548.4). Exposure-response relationships were demonstrated for both disease outcomes, with nearly sixfold and threefold increased risks seen at the highest exposure level for lung cancer deaths and asbestosis, respectively.

Conclusion: Evidence using quantitative exposure estimates was provided for increased risks of lung cancer mortality and development of asbestosis in a predominantly chrysotile-exposed cohort.

© 2016 Wiley Periodicals, Inc.

In plain English

This study followed 577 male workers at a chrysotile asbestos products factory in Chongqing, China, from 1972 through 2008. The factory made asbestos textiles, rubber products and asbestos cement. The authors converted historical dust measurements into estimated airborne fiber levels and calculated each worker's cumulative exposure. The median was 132.6 fiber-years/ml when exposure was lagged by 10 years. During follow-up there were 55 lung cancer deaths and 127 diagnosed cases of asbestosis. The analysis took age and smoking into account. Compared with the lowest-exposed group, workers in the highest exposure quarter had a hazard ratio of 5.59 (95% CI 4.77 to 6.56) for lung cancer death and 3.09 (2.94 to 3.25) for asbestosis. For each 100 fiber-years/ml, the hazard ratio was 1.098 (1.090 to 1.107) for lung cancer death and 1.055 (1.052 to 1.058) for asbestosis. Only two mesotheliomas occurred, which was too few to analyze. The authors concluded that chrysotile exposure is associated with an increased risk of lung cancer death and asbestosis. They noted uncertainties in their exposure estimates. They also noted that a separate study found tremolite in factory air samples from 2006.

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 using estimated individual cumulative fiber exposures and Cox proportional hazards models with age as the time scale and smoking as a covariate
• Who was studied: 586 male workers at an asbestos products factory in Chongqing, China, who had been on the employment roster for at least 1 year as of January 1, 1972, with no signs of cardiopulmonary disease. They were followed through December 31, 2008, and 577 (99%) were successfully followed up.
• Exposure: Chrysotile asbestos used in making textiles, rubber products and asbestos cement. The authors state that the factory never used amphibole asbestos as a feedstock. Median cumulative exposure was 137.5 fiber-years/ml with no lag and 132.6 fiber-years/ml with a 10-year lag.
• Main results:
  • There were 259 deaths in the cohort, including 98 cancer deaths, of which 55 were from lung cancer. There were 127 diagnosed cases of asbestosis.
  • Median cumulative exposure was 137.5 fiber-years/ml (range 28.1 to 2113.0) with no lag and 132.6 fiber-years/ml (range 0 to 2108.8) with a 10-year lag. The 10-year lag was used for the main analyses.
  • Treating exposure as a continuous measure, the hazard ratio for every 100 fiber-years/ml was 1.098 (1.090 to 1.107) for lung cancer death and 1.055 (1.052 to 1.058) for developing asbestosis.
  • Lung cancer death, compared with the lowest exposure group (0 to under 89 fiber-years/ml, which included administration and rear service workers), by exposure quarter: second quarter (89 to under 133) hazard ratio 1.93 (95% CI 1.07 to 2.32); third quarter (133 to under 548) 2.59 (2.18 to 3.09); fourth quarter (548 and above) 5.59 (4.77 to 6.56).
  • Asbestosis, compared with the lowest exposure group, by exposure quarter: second quarter hazard ratio 2.26 (95% CI 2.14 to 2.38); third quarter 2.71 (2.57 to 2.85); fourth quarter 3.09 (2.94 to 3.25). Trend tests for both outcomes were significant at P less than 0.001.
  • Lung cancer deaths by exposure quarter: 10 of 231 workers in the first, 9 of 112 in the second, 13 of 118 in the third and 23 of 116 in the fourth. Asbestosis cases: 21 of 231, 30 of 112, 34 of 118 and 42 of 116.
  • Smoking (ever smokers) was associated with increased risk. The hazard ratio was 3.15 (95% CI 2.60 to 3.81) for lung cancer death and 1.94 (1.84 to 2.04) for asbestosis.
  • Two mesothelioma cases occurred. This was too few for mesothelioma to be evaluated as an outcome.
• The authors' conclusion: The authors concluded that the study adds to evidence that chrysotile exposure is associated with an increased risk of lung cancer death and development of asbestosis, and that an exposure-response relationship was demonstrated for both outcomes.
• Limitations the authors state:
  • Recent paired fiber and dust measurements (from 1999 and 2002) were used to convert historical dust measurements going back to 1955 into fiber levels. No paired samples from earlier periods were available to check whether the dust-to-fiber ratio changed over time.
  • Fiber and dust levels did not match well in the rubber and cement workshops, possibly because of other materials such as sand, rubber and mica.
  • Maintenance workers were assigned the weavers' exposure levels, which increased uncertainty in their exposure estimates.
  • No samples were taken in the offices of administration and rear service workers. These workers were assigned the lowest non-zero exposure value, which could be an underestimate.
  • Some workers manually spun chrysotile at home into the 1970s. It is unknown who did so, which may have led to exposure being underestimated for some cohort members.
  • The purity of the chrysotile has been questioned. A separate study of airborne fibers at this factory found tremolite contamination in samples collected in 2006.
  • Smoking was recorded only as ever or never, not as a quantitative measure such as pack-years.
  • The Chinese diagnostic criteria classify a profusion of 1/0 as negative. The authors state this likely led to under-diagnosis of asbestosis and a conservative estimate of asbestosis risk.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Chrysotile, Cumulative Exposure, Occupational History, Hazard Ratio, Fiber Year.

Related studies

• Cause-specific mortality in relation to chrysotile-asbestos exposure in a Chinese cohort — S. Lin, X. Wang, et al. (2012)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)
• Exposure to chrysotile mining dust and digestive cancer mortality in a Chinese miner/miller cohort — S. Lin, X. Wang, et al. (2014)
• 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)
• A 37-year observation of mortality in Chinese chrysotile asbestos workers — X. Wang, E. Yano, et al. (2012)

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