Cancer mortality and asbestosis among workers in an asbestos plant in Chongqing, China

Our plain-English summary of Cancer mortality and asbestosis among workers in an asbestos plant in Chongqing, China, by F. Zhong, E. Yano, Z.M. Wang, et al (Biomedical and Environmental Sciences, 2008).

The study

• Authors: F. Zhong, E. Yano, Z.M. Wang, M.Z. Wang, Y.J. Lan
• Journal: Biomedical and Environmental Sciences
• Published: 2008;21(3):205-11
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To investigate whether asbestosis is a risk factor for mortality of lung cancer.

Methods: A fixed cohort study was established in an asbestos plant in Chongqing, China, and followed up for 30 years from the beginning of 1972. Basic personal information on life state, cause of death, and diagnosis of asbestosis was collected. Multiple logistic regressions were applied to analyze risk factors.

Results: During the 30-year follow-up, 584 male workers constituting a total of 14,664 person-years were monitored and data were analyzed. Among them, 203 (34.8%) died and the mortality rate was 13.8 per 1000 person-years, cancer accounting for 37.4%. Excess risks were observed for lung cancer (OR = 3.72) and nonmalignant respiratory diseases (OR = 2.73) among workers with asbestosis. High-exposure level was another risk factor for lung cancer (OR = 3.20). Workers with category II of asbestosis demonstrated a higher OR of both lung cancer and nonmalignant respiratory diseases than those with category I of asbestosis.

Conclusion: High asbestos exposure level and asbestosis were the risk factors for death of lung cancer and nonmalignant respiratory diseases. Asbestosis is an independent risk factor for lung cancer among Chinese workers exposed to chrysotile, the risk increases with the increasing profusion of opacities of lung.

In plain English

This retrospective cohort study followed 584 male workers at a Chongqing, China, asbestos plant from 1972 to 2001. The plant used Chinese chrysotile containing only 0.001% tremolite. Exposure was ranked high, intermediate or low by job section; asbestosis was graded category I or II under Chinese X-ray criteria. Of the 584 workers, 203 (34.8%) died. Seventy-six deaths were from cancer, including 38 lung cancer and 2 mesothelioma deaths (one pleural, one peritoneal). The death rate per 1000 person-years was 21.4 for workers with asbestosis and 11.6 for those without. After adjusting for smoking, age at hiring, years worked and exposure level, workers with asbestosis had higher odds of lung cancer death (OR=3.72, 95% CI 1.73 to 7.97; mesothelioma was counted with lung cancer) and of nonmalignant respiratory disease death (OR=2.73, 95% CI 1.51 to 4.92). High exposure was linked to lung cancer death (OR=3.20, 95% CI 1.01 to 10.19). Both odds were higher for category II than category I. The authors concluded asbestosis was an independent risk factor for lung cancer. They noted Chinese criteria may have undercounted asbestosis.

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 study with follow-up from January 1, 1972 to December 31, 2001. Risk factors were analysed by multiple logistic regression.
• Who was studied: 584 male workers at an asbestos plant in Chongqing, China. They were registered before 1 January 1972, had worked more than 1 year and had no evident signs of severe cardiopulmonary disease. They gave 14 664 person-years of observation. Of these, 120 had asbestosis (100 category I, 20 category II), 452 did not, and asbestosis data were missing for 12.
• Exposure: Chrysotile asbestos from Chinese mines, containing 0.001% tremolite fibers, used to make a wide variety of asbestos products. Workers were classed by job into three exposure levels: high (raw material, card and weave sections), intermediate (other sections) and low (office and asbestos cement sections). Dust concentration was 146.2 (32.8 to 230.4) mg/m3 before the 1960s and below 10 mg/m3 in the 1990s.
• Main results:
  • Of the 584 workers, 203 (34.8%) died, a mortality rate of 13.8 per 1000 person-years.
  • There were 76 cancer deaths, of which 38 were from lung cancer. Two deaths were from mesothelioma, one pleural and one peritoneal.
  • The mortality rate was 11.6 per 1000 person-years for workers without asbestosis and 21.4 per 1000 person-years for workers with asbestosis.
  • Workers with asbestosis had higher odds of lung cancer death than workers without asbestosis (OR=3.72, 95% CI 1.73 to 7.97). This was after adjusting for smoking, age at employment, exposure duration and exposure level. Mesothelioma was included with lung cancer in this analysis.
  • A high exposure level was associated with lung cancer death (OR=3.20, 95% CI 1.01 to 10.19).
  • Asbestosis was associated with death from nonmalignant respiratory diseases (OR=2.73, 95% CI 1.51 to 4.92 in Table 3).
  • For death from all cancers combined, the odds ratio for asbestosis was 1.57 (95% CI 0.88 to 2.82, p=0.128). This was not statistically significant.
  • Smoking had an odds ratio above 1 for lung cancer death (OR=2.82, 95% CI 0.83 to 9.63). The authors state that smoking was not a significant risk factor in this cohort.
  • Compared with workers without asbestosis, the odds of lung cancer death were 3.62 (95% CI 1.63 to 8.04) for category I asbestosis and 4.26 (95% CI 1.07 to 16.97) for category II.
  • For death from nonmalignant respiratory disease, the odds ratio was 5.04 (95% CI 1.68 to 15.12) for category II and 2.41 (95% CI 1.28 to 4.52) for category I.
• The authors' conclusion: The authors concluded that heavy asbestos exposure and asbestosis were risk factors for lung cancer death. In their view, asbestosis is an independent risk factor for lung cancer among Chinese workers exposed to chrysotile, and the risk increases with the profusion of radiological lung opacities.
• Limitations the authors state:
  • Asbestosis was diagnosed under the Chinese criteria (GB5908-86) rather than the ILO classification. Because ILO category 1/0 does not count as pneumoconiosis under the Chinese criteria, the number of workers with asbestosis may be underestimated.
  • Because of the different diagnostic criteria, the results cannot be directly compared with studies that used the ILO classification. The authors call for further study that measures fiber concentration and uses the ILO classification.
  • Survival analysis could not be used because the date of asbestosis diagnosis was not available. Logistic regression was used instead.

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, Cohort Study, Asbestos Exposure, Chrysotile.

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