Exposure to chrysotile mining dust and digestive cancer mortality in a Chinese miner/miller cohort

Our plain-English summary of Exposure to chrysotile mining dust and digestive cancer mortality in a Chinese miner/miller cohort, by S. Lin, X. Wang, E. Yano, et al (Occupational and Environmental Medicine, 2014).

The study

• Authors: S. Lin, X. Wang, E. Yano, I. Yu, Y. Lan, M.N. Courtice, D.C. Christiani
• Journal: Occupational and Environmental Medicine
• Published: 2014;71(5):323-8
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: To examine mortality from digestive cancers in a Chinese miner cohort and to explore the exposure-response relationship between chrysotile mining dust and site-specific digestive cancers.

Methods: A cohort of 1539 asbestos miners was followed for 26 years. Information on vital status and death causes was collected from personnel records and hospitals. Underlying causes of death from cancers were determined by combination of clinical manifestations and pathological confirmation. Individual cumulative dust exposures were estimated based on periodic dust measurements of different workshops, individuals' job title and employment duration, and treated as a time-dependent variable. Standardised mortality ratios (SMR) were calculated according to Chinese national data and stratified by exposure (levels 1-3, from low to high). Cox proportional hazard models were constructed to estimate HRs in relation to cumulative exposure with adjustment of smoking.

Results: Fifty-one deaths from digestive cancers were identified in the cohort, giving an SMR of 1.45 (95% CI 1.10 to 1.90). There was a clear exposure-response relationship between asbestos dust exposure and mortality from stomach cancer, with SMR of 2.39 (95% CI 1.02 to 5.60) and 6.49 (2.77 to 15.20) at exposure levels 2 and 3, respectively. The clear relationship remained in multivariate analysis, in which workers at the highest exposure level had HRs of 12.23 (95% CI 8.74 to 17.12). In addition, excess mortality from oesophageal and liver cancers was also observed at high exposure levels.

Conclusions: This study provides additional evidence for the association between exposure to chrysotile mining dust and excess mortality from digestive cancers, particularly stomach cancer.

In plain English

This retrospective cohort study followed 1539 male workers at China's largest chrysotile asbestos mine from 1981 to 2006. Analysed mine samples detected no tremolite, at a detection limit of 0.1%. Cumulative dust exposure was estimated from workshop measurements and job histories. There were 51 digestive cancer deaths, a standardised mortality ratio (SMR) of 1.45 (95% CI 1.10 to 1.90) versus Chinese national rates. Overall, stomach cancer deaths were 50% above expected, which was not statistically significant. Stomach cancer mortality rose with exposure: SMRs were 2.39 (1.02 to 5.60) at the middle exposure level and 6.49 (2.77 to 15.20) at the highest. Adjusted for smoking, the stomach cancer hazard ratio at the highest versus lowest level was 12.23 (8.74 to 17.12). Oesophageal and liver cancer SMRs were significantly raised only at the middle level, with no clear trend, though within-cohort risks were higher at both upper levels. The authors concluded the findings supported a positive association between chrysotile mining dust and stomach cancer. They noted few deaths, area-based exposure estimates, and no data on alcohol, Helicobacter pylori or hepatitis.

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 cohort mortality study. It compared the cohort with Chinese national male death rates (SMRs) and compared exposure levels within the cohort using Cox models adjusted for smoking.
• Who was studied: 1539 male workers at a chrysotile asbestos mine in Qinghai Province, China, who had worked there at least 1 year by 1 January 1981 and were followed to 31 December 2006 (34 736 person-years, no one lost to follow-up).
• Exposure: Chrysotile mining and milling dust (total asbestos dust). Analysis of asbestos samples from the mine detected no tremolite at a detection limit of 0.1%. Individual cumulative exposure in mg-years/m3 was estimated from workshop area measurements and job history; geometric mean 108.7, range 1.8 to 3613.5.
• Main results:
  • Whole cohort: 51 digestive cancer deaths against 35.27 expected, SMR 1.45 (95% CI 1.10 to 1.90).
  • Whole cohort: stomach cancer mortality was 50% higher than expected, with a confidence interval that included no excess (0.91 to 2.47).
  • Stomach cancer compared with the general population: SMR 2.39 (95% CI 1.02 to 5.60) at exposure level 2 and 6.49 (2.77 to 15.20) at level 3.
  • Stomach cancer within the cohort, adjusted for smoking, compared with level 1: HR 4.74 (3.38 to 6.65) at level 2 and 12.23 (8.74 to 17.12) at level 3.
  • Oesophageal and liver cancer compared with the general population: mortality was significantly raised only at exposure level 2, with no evident exposure-response trend.
  • Oesophageal and liver cancer within the cohort, adjusted for smoking: risk was significantly higher at exposure levels 2 and 3 than at level 1.
  • Smoking was not significantly associated with death from any of these cancers.
• The authors' conclusion: The authors concluded that heavily exposed chrysotile miners and millers had excess mortality from stomach, oesophageal and liver cancers. In their view, the clear exposure-response trend for stomach cancer supported a positive association between chrysotile mining dust and stomach cancer.
• Limitations the authors state:
  • Exposures were estimated from area (fixed-point) sampling rather than individual samples, which might have caused exposure misclassification.
  • The small number of digestive cancer deaths limited study power and widened confidence intervals.
  • There were no data on alcohol, Helicobacter pylori infection or hepatitis B and C infection, which could be confounders.
  • Metastatic lung cancer might have been misclassified as digestive cancer.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Cumulative Exposure, Stomach Cancer, Multivariate Analysis.

Related studies

• 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)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 — J.C. McDonald, F.D. Liddell, et al. (1993)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• Cause-specific mortality in a Chinese chrysotile textile worker cohort — X. Wang, S. Lin, et al. (2013)
• Exposure-specific lung cancer risks in Chinese chrysotile textile workers and mining workers — X. Wang, S. Lin, et al. (2014)

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