Mesothelioma and lung cancer mortality: a historical cohort study among asbestosis workers in Hong Kong

Our plain-English summary of Mesothelioma and lung cancer mortality: a historical cohort study among asbestosis workers in Hong Kong, by M. Chen, L.A. Tse, R.K. Au, et al (Lung Cancer, 2012).

The study

• Authors: M. Chen, L.A. Tse, R.K. Au, I.T. Yu, X.R. Wang, X.Q. Lao, J.S. Au
• Journal: Lung Cancer
• Published: 2012;76(2):165-70
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: To investigate the mortality pattern among a cohort of workers with asbestosis in Hong Kong, with special emphases on mesothelioma and lung cancer.

Methods: All 124 male workers with confirmed asbestosis in Hong Kong during 1981-2008 were followed up to December 31, 2008 to ascertain the vital status and causes of death. Standardized mortality ratio (SMR) for each underlying cause of death was calculated by using person-year method. Axelson's indirect method was applied to adjust for the potential confounding effect of cigarette smoking.

Results: A total of 86 deaths were observed after 432.8 person-years of observations. The SMR for overall mortality (6.06, 95% CI: 4.90-7.51) increased significantly. The elevated risk of deaths from all cancers (7.53, 95% CI: 5.38-10.25) was mainly resulted from a significantly excess risk from lung cancer (SMR=7.91, 95% CI: 4.32-13.29, 14 deaths) and mesothelioma (SMR=6013.63, 95% CI: 3505.95-9621.81, 17 deaths). The SMR for lung cancer retained statistically significant after adjustment of smoking. An increased smoking adjusted SMR was also suggested for all heart diseases (2.32, 95% CI: 0.93-4.79, 7 deaths) and acute myocardial infarction (3.10, 95% CI: 0.84-7.94, 4 deaths), though the statistical significance was borderline. We found a positive association with net years of exposure to asbestos for mesothelioma and lung cancer.

Conclusions: Our study provided further evidence on the carcinogenesis of asbestos/asbestosis with the risk of deaths from lung cancer and mesothelioma. This study also provided a preliminary support for a possible link between asbestosis and heart disease, but power is limited.

Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

In plain English

This historical cohort study followed all 124 men newly diagnosed with asbestosis at Hong Kong's Pneumoconiosis Clinic between 1981 and 2008 until the end of 2008. Deaths were compared with male general population rates. Most worked in shipyards or construction, averaging 31.49 years in asbestos-related jobs. Of the men whose smoking status was recorded, 106 had ever smoked and 9 were non-smokers. There were 86 deaths in 432.8 person-years, and all-cause deaths were 6.06 times expected (95% CI 4.90 to 7.51). Fourteen men died of lung cancer (SMR 7.91, 95% CI 4.32 to 13.29). Adjusted indirectly for smoking, it remained raised at 3.72 (95% CI 2.03 to 6.26). Seventeen died of mesothelioma against 0.0028 expected (SMR 6013.63, 95% CI 3505.95 to 9621.81). The authors had no information on mesothelioma site. Heart disease deaths were raised, but after smoking adjustment the excess was borderline (2.32, 95% CI 0.93 to 4.79). Longer exposure was suggested to go with higher lung cancer and mesothelioma ratios. The authors concluded the lung cancer and mesothelioma associations may reflect the truth, and that heart disease support was preliminary, with limited power.

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: Historical (retrospective) cohort study comparing deaths with the Hong Kong male general population using standardized mortality ratios (SMR), with indirect adjustment for smoking (Axelson's method)
• Who was studied: All 124 male workers newly diagnosed with asbestosis at the Pneumoconiosis Clinic of the Hong Kong Department of Health between 1981 and 2008, followed to December 31, 2008. The first case was registered in 1986. There were 432.8 person-years of observation, 6 men were lost to follow-up, and 86 died. Mean age at diagnosis was 71.68 years. Table 1 lists 106 ever smokers (92.17%) and 9 non-smokers (7.83%), so smoking status is not given for every one of the 124 men.
• Exposure: Occupational asbestos exposure, measured as net years in asbestos-related jobs (mean 31.49) and age at first exposure (mean about 19.94 years). Main occupations: shipyard (44.4%), construction site (21.6%), manufacturing (11.4%), mechanical (7.1%), mining (5.2%), electricity (4.0%) and other (6.3%). No fiber-type or concentration data were collected for the cohort.
• Main results:
  • All causes of death in the whole cohort: SMR 6.06 (95% CI 4.90 to 7.51), based on 86 deaths
  • All cancers in the whole cohort: 36 deaths, SMR 7.53 (95% CI 5.38 to 10.25)
  • In the whole cohort, there were 17 mesothelioma deaths (SMR 6013.63, 95% CI 3505.95 to 9621.81) and 14 lung cancer deaths (SMR 7.91, 95% CI 4.32 to 13.29). Mesothelioma deaths were counted under ICD-9 code 163.
  • Asbestosis as cause of death in the whole cohort: 21 deaths against 0.029 expected, SMR 713.17 (95% CI 441.45 to 1091.15)
  • After indirect adjustment for smoking, SMRs stayed statistically significant for lung cancer (3.72, 95% CI 2.03 to 6.26) and tuberculosis (11.53, 95% CI 2.37 to 33.67). They were 4.19 (3.39 to 5.19) for all deaths and 4.85 (3.46 to 6.59) for all cancers.
  • Heart disease (7 deaths) unadjusted SMR was 3.24 (95% CI 1.30 to 6.67) and acute myocardial infarction (4 deaths) was 4.32 (1.17 to 11.05). After smoking adjustment these became borderline: 2.32 (0.93 to 4.79) and 3.10 (0.84 to 7.94).
  • When cigarette smoking and other major confounding factors were taken into account, the lung cancer SMR was 3.15 (95% CI 1.69 to 5.22)
  • After excluding the 20 workers who already had cancer when asbestosis was diagnosed, SMRs were lower. Table 2 gives lung cancer 7.44 (95% CI 3.85 to 13.02, 12 deaths) and mesothelioma 3118.43 (1556.10 to 5581.99, 8 deaths).
  • A positive association with net years of exposure was suggested. Lung cancer SMR was 7.26 (5 deaths) for under 30 years versus 8.33 (9 deaths) for 30 years or more. Mesothelioma SMR was 4634.25 (5 deaths) versus 6865.03 (12 deaths).
• The authors' conclusion: The authors concluded that the strong association with deaths from lung cancer and mesothelioma may reflect the truth, because the cohort is less selective and smoking and other confounders were reasonably considered. They also concluded the study offered preliminary support for a possible link between asbestosis and heart disease mortality, with limited power.
• Limitations the authors state:
  • No data on asbestos concentrations were collected, and years of exposure may not adequately represent lifetime exposure
  • No information on the site of the mesothelioma
  • Limited power for the heart disease findings because of the small number of deaths
  • Possible selection bias, since cases came from a compensation registry; the authors argued this was less likely in Hong Kong
  • Whether asbestosis is a prerequisite for mesothelioma could not be determined without a comparison group of exposed workers without asbestosis
  • Misclassification of the underlying cause of death was possible, though the authors judged it not serious

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Lung Cancer, Cohort Study, standardized mortality ratio (SMR), Confounding, Statistical Significance, Carcinogenesis.

Related studies

• Are current or future mesothelioma epidemics in Hong Kong the tragic legacy of uncontrolled use of asbestos in the past? — L.A. Tse, I.T. Yu, et al. (2010)
• Malignant mesothelioma in Hong Kong — K.C. Chang, C.C. Leung, et al. (2006)
• History of Asbestos Ban in Hong Kong — C.K. Wong, S.H. Wan, et al. (2017)
• Asbestos fiber burdens in lung tissues of Hong Kong Chinese with and without lung cancer — Y. Liu, P. Zhang, et al. (2001)
• A historical cohort mortality study among shipyard workers in Genoa, Italy — R. Puntoni, F. Merlo, et al. (2001)
• Historical cohort study of US man-made vitreous fiber production workers: II. Mortality from mesothelioma — G.M. Marsh, M.J. Gula, et al. (2001)

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