Cancer Attributable to Asbestos Exposure in Shipbreaking Workers: A Matched-Cohort Study

Our plain-English summary of Cancer Attributable to Asbestos Exposure in Shipbreaking Workers: A Matched-Cohort Study, by W.T. Wu, Y.J. Lin, C.Y. Li, et al (PloS One, 2015).

The study

• Authors: W.T. Wu, Y.J. Lin, C.Y. Li, P.J. Tsai, C.Y. Yang, S.H. Liou, T.N. Wu
• Journal: PloS One
• Published: 2015;10(7):e0133128
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: Long-term follow-up studies of asbestos-related cancer in shipbreaking workers are lacking. This study examines the relationship between cancer incidence and asbestos exposure among former Taiwan shipbreaking workers.

Methods: A total of 4,427 shipbreaking workers and 22,135 population-based matched controls were successfully followed in this study. The study cohort was linked to the Taiwan Cancer Registry for new cancer cases. The adjusted hazard ratio (aHR) for cancer was calculated for the shipbreaking workers with Total Exposure Potential Scores (TEP) for asbestos.

Results: Follow-up generated 109,932 person-years, with 940 deaths and 436 cancer cases, among 4,427 shipbreaking workers from 1985 to 2008. The high asbestos exposure group also had a statistically significant increase in the risk of overall cancer (aHR= 1.71; 95% CI: 1.42-2.05), esophagus cancer (aHR= 2.31; 95% CI: 1.00-5.41), liver and intrahepatic bile duct cancer (aHR= 1.60; 95% CI: 1.08-2.36), and trachea, bronchus, and lung cancer (aHR= 3.08; 95% CI: 1.80-5.25). Mesothelioma cases were found in the high asbestos exposure group. Moreover, overall cancer, esophagus cancer, and trachea, bronchus, and lung cancer were seen in a dose-dependent relationship with asbestos exposure.

Conclusions: This study presented the elevated trend of asbestos exposure with cancer incidence for overall cancer, esophagus cancer, and trachea, bronchus, and lung cancer among shipbreaking workers. Those workers previously exposed to asbestos should receive persistent monitoring in order to early detect adverse health outcomes.

In plain English

This retrospective matched-cohort study followed 4,427 former shipbreaking workers in Taiwan, members of the 1985 Kaohsiung Shipbreaking Workers Union, and 22,135 general-population controls matched by age, sex and living area. All were linked to the Taiwan Cancer Registry through 2008. Asbestos exposure was estimated from expert ratings of eight job titles, weighted by the tonnage of ships broken each year and summed over years worked. Of the workers, 436 (9.9%) developed cancer, compared with 1,488 (6.7%) of controls. Compared with controls, workers had higher adjusted hazard ratios for all cancers (1.63; 95% CI 1.46–1.81) and for trachea, bronchus and lung cancer (2.71; 1.99–3.69). In the high-exposure group the ratio was 3.08 (1.80–5.25) for lung cancer and 2.31 (1.00–5.41) for esophagus cancer. Risks of all cancers, esophagus cancer and lung cancer rose with exposure level. Two mesothelioma cases were found among flame cutters and in the high-exposure group. The authors concluded that overall, esophagus, and trachea, bronchus and lung cancer were associated with exposure level. They had no data on smoking, alcohol or diet. Apart from a single 1987 workplace survey, they had no historical exposure records.

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 matched-cohort study linking a worker cohort and general-population controls to the national cancer registry
• Who was studied: 4,427 shipbreaking workers in Taiwan, members of the 1985 Kaohsiung Shipbreaking Workers Union, first employed from 1975 and followed to 31 December 2008 (89.2% follow-up rate). Each worker was matched to five general-population controls with the same age, sex and living area, for 22,135 controls in total. 84.3% of the workers were men.
• Exposure: Asbestos exposure in shipbreaking, scored by a seven-expert panel for eight job titles. Flame cutters scored highest (9.6) and administrators lowest (2.1). The scores were weighted by the gross tonnage of ships broken each year and summed over years of employment to give a Total Exposure Potential Score (TEP). Workers were grouped as low (under 32.86 TEP), medium (32.86 to 45.45) and high (45.46 or more). The expert scores correlated with a single 1987 workplace survey of air concentrations (R = 0.878), particularly for amosite and crocidolite. Mean exposure duration was 6.9 years.
• Main results:
  • 436 of 4,427 shipbreaking workers (9.9%) had cancer, compared with 1,488 of 22,135 controls (6.7%); p less than 0.001. Follow-up of the workers totalled 109,932 person-years, with 940 deaths among them.
  • All shipbreaking workers compared with controls, adjusted for monthly ratable wage: overall cancer aHR 1.63 (95% CI 1.46–1.81); oral cavity 2.47 (1.89–3.21); nasopharynx 2.18 (1.39–3.42); liver and intrahepatic bile duct 1.50 (1.16–1.94); trachea, bronchus and lung 2.71 (1.99–3.69); unknown primary 4.18 (1.66–10.5).
  • High asbestos exposure group compared with matched controls: overall cancer aHR 1.71 (95% CI 1.42–2.05); esophagus 2.31 (1.00–5.41); liver and intrahepatic bile duct 1.60 (1.08–2.36); trachea, bronchus and lung 3.08 (1.80–5.25); thymus, heart and mediastinum 8.83 (1.19–65.7).
  • Overall cancer, esophagus cancer, and trachea, bronchus and lung cancer showed excess risk that increased with asbestos exposure group.
  • Two mesothelioma cases were found among flame cutters and in the high asbestos exposure group. The hazard ratio for mesothelioma in all workers was 8.55 (95% CI 0.53–138.9), which was not statistically significant.
  • Workers were diagnosed younger than controls for overall cancer (mean 54.5 vs 57.0 years), liver and intrahepatic bile duct cancer (53.1 vs 56.8) and trachea, bronchus and lung cancer (59.7 vs 63.6).
  • Flame cutters (n = 2,609) had a statistically significant increase for overall cancer and for oral, nasopharyngeal, esophagus, stomach, liver and intrahepatic bile duct, trachea, bronchus and lung, and thymus, heart and mediastinum cancers. Their lung cancer HR was 3.15 (2.01–4.92).
• The authors' conclusion: The authors concluded that increased incidence of overall cancer, esophagus cancer, and trachea, bronchus and lung cancer was associated with the level of asbestos exposure among shipbreaking workers. They stated that previously exposed workers should be monitored.
• Limitations the authors state:
  • No information on smoking, alcohol or diet. The authors could not entirely exclude an effect of alcohol.
  • Historical exposure data were lacking (only one workplace survey, from 1987, exists), so the study relied on the TEP score to represent long-term exposure.
  • No information on whether workers changed jobs during their exposure period, which could cause underestimation.
  • The comparison group was the general population. Asbestos exposure among controls and the healthy worker effect could both lead to underestimated results.
  • The supervisor group (n = 42) was small, which might explain its high cancer estimates.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Cohort Study, Cancer Registry, Hazard Ratio, Bronchus, Lung Cancer, Mesothelioma.

Related studies

• Cancer incidence of Taiwanese shipbreaking workers who have been potentially exposed to asbestos — W.T. Wu, Y.J. Lin, et al. (2014)
• Mortality among shipbreaking workers in Taiwan--a retrospective cohort study from 1985 to 2008 — W.T. Wu, Y.H. Lu, et al. (2013)
• Cancer incidence among Swedish pulp and paper mill workers: a cohort study of sulphate and sulphite mills — E. Andersson, H. Westberg, et al. (2013)
• Mortality and cancer morbidity in a cohort of Canadian petroleum workers — R.J. Lewis, A.R. Schnatter, et al. (2003)
• Cancer risks in a historical UK cohort of benzene exposed workers — T. Sorahan, L.J. Kinlen, et al. (2005)
• Risk of cancer among Danish utility workers--a nationwide cohort study — C. Johansen, J.H. Olsen (1998)

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