Cancer incidence of Taiwanese shipbreaking workers who have been potentially exposed to asbestos

Our plain-English summary of Cancer incidence of Taiwanese shipbreaking workers who have been potentially exposed to asbestos, by W.T. Wu, Y.J. Lin, H.S. Shiue, et al (Environmental Research, 2014).

The study

• Authors: W.T. Wu, Y.J. Lin, H.S. Shiue, C.Y. Li, P.J. Tsai, C.Y. Yang, S.H. Liou, T.N. Wu
• Journal: Environmental Research
• Published: 2014;132:370-8
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Shipbreaking remains one of the most dangerous jobs worldwide. Shipbreaking workers are exposed to many hazardous chemicals, especially asbestos. Unfortunately, long-term follow-up studies of cancer incidence patterns in shipbreaking workers are lacking. This study examines whether there is an increased risk of cancer among male shipbreaking workers over a 24-year follow-up period.

Methods: 4155 male shipbreaking worker's information was retrospectively collected from Kaohsiung's Shipbreaking Workers Union database from 1985. The study cohort was linked to the Taiwan Cancer Registry from 1985 to 2008 for new cancer cases. The expected number of cancers for shipbreaking workers was calculated by using the age (5-year intervals) and calendar time-specific annual rates of cancer incidence with reference to the general population of Taiwan from 1985 to 2008. Standardized incidence ratios (SIRs) were calculated as relative risk estimates. The hazard ratio (HR) for cancer was calculated for the shipbreaking workers with Total Exposure Potential Scores for asbestos.

Results: After consideration of a 5-year latency period, an elevated incidence of overall cancer (N=368; SIR=1.13 (1.01-1.25)), oral cavity cancer (N=83; SIR=1.99 (1.58-2.46)), and trachea, bronchus, and lung cancers (N=53; SIR=1.36 (1.02-1.78)) was found among male shipbreaking employees. Moreover, mesothelioma cases were found in those who had the occupation of flame cutter. The high asbestos exposure group was associated with an increased SIR of developing overall cancer and oral cancer, whether we considered a 5-year or 10-year latency period.

Conclusion: Asbestos-related diseases, including lung cancer and mesothelioma, were seen in excess in these shipbreaking workers and some cases appeared to have a dose-dependent relationship. Preventative measures among male shipbreaking workers should be researched further.

Copyright © 2014 Elsevier Inc. All rights reserved.

In plain English

This retrospective cohort study followed 4155 male members of the 1985 Kaohsiung Shipbreaking Workers Union. The authors linked them to the Taiwan Cancer Registry for cancers diagnosed from 1985 to 2008 and compared their rates with Taiwan's general population. Seven experts scored asbestos exposure for eight job titles, checked against 1987 harbor sampling for chrysotile, amosite and crocidolite. Counting cancers at least 5 years after first employment, workers had more cancer overall than expected (368 cases; SIR 1.13, 95% CI 1.01 to 1.25). They also had more oral cavity cancer (83 cases; SIR 1.99, 1.58 to 2.46) and trachea, bronchus and lung cancer (53 cases; SIR 1.36, 1.02 to 1.78). Overall cancer was significantly raised in the high asbestos exposure group, and oral cancer in all three exposure groups; Cox models of exposure scores found no statistically significant increase. Mesothelioma, with too few cases to report exactly, appeared in flame cutters and the high-exposure group. The authors concluded that lung cancer and mesothelioma were seen in excess. They noted missing personal sampling and smoking, alcohol and diet data.

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 24 years of follow-up, linking a union membership list to the national cancer registry and comparing workers with the general population using standardized incidence ratios (SIRs) and Cox hazard models
• Who was studied: 4155 male shipbreaking workers who were members of the 1985 Kaohsiung Shipbreaking Workers Union in Taiwan, employed for over a year, first employed from 1975 onward; followed for new cancers from 1 January 1985 to 31 December 2008. Women (805) were excluded.
• Exposure: Asbestos exposure in shipbreaking. A panel of seven experts rated exposure intensity for eight job titles on a 0 to 10 scale: flame cutters 9.6, odd-jobbers 7.1, sorters 6.0, lifters 5.7, supervisors 5.6, knockers 4.6, drivers 2.6, administrators 2.1. The authors checked these ratings against 1987 sampling of 91 areas of Kaohsiung harbor for asbestos, chrysotile, amosite and crocidolite. They then combined the ratings with years worked and the tonnage of ships broken each year into Total Exposure Potential Scores, grouped as low, medium and high.
• Main results:
  • With a 5-year latency period, all male workers had an elevated incidence of overall cancer: 368 cases, SIR 1.13 (95% CI 1.01 to 1.25).
  • With a 5-year latency period, all male workers had an elevated incidence of oral cavity cancer: 83 cases, SIR 1.99 (1.58 to 2.46).
  • With a 5-year latency period, all male workers had an elevated incidence of trachea, bronchus and lung cancer: 53 cases, SIR 1.36 (1.02 to 1.78).
  • The workers had a statistically significant decrease in rectal cancer: 10 cases, SIR 0.51 (0.25 to 0.94).
  • With a 10-year latency period, the SIR for overall cancer was 1.06 (0.95 to 1.18) and for trachea, bronchus and lung cancer 1.31 (0.97 to 1.72). The authors stated these were not statistically significant.
  • In the whole cohort, mesothelioma had an SIR of 10.7 (0.14 to 59.6). The number of cases was marked as fewer than 2 because of a privacy rule.
  • Flame cutters (5-year latency) had a statistically significant increase in overall cancer: 236 cases, SIR 1.24 (1.08 to 1.41). Their oral cavity cancer was also increased: 50 cases, SIR 1.77 (1.31 to 2.33). Mesothelioma in flame cutters had an SIR of 18.74 (0.25 to 104.2).
  • The high asbestos exposure group had an increased SIR for overall cancer: 1.26 (1.07 to 1.48) with a 5-year latency and 1.21 (1.02 to 1.43) with a 10-year latency. It also had an increased SIR for oral cancer.
  • Mesothelioma cases were found only in the high asbestos exposure group, with an SIR of 29.1 (0.38 to 161).
  • In the high asbestos exposure group, the increase in trachea, bronchus and lung cancer was not statistically significant (5-year latency: 20 cases, SIR 1.52, 0.93 to 2.35).
  • Oral cavity cancer was significantly increased in all three asbestos exposure groups (low, medium and high).
  • Cox models found no statistically significant increase in hazard ratio for any cancer with total Exposure Potential Scores for asbestos, including after adjustment for age at first employment, residence area and wage. There was also no significant increase with duration of employment.
• The authors' conclusion: The authors concluded that asbestos-related diseases, including lung cancer and mesothelioma, were seen in excess in these shipbreaking workers, and that some cases appeared to have a dose-dependent relationship. They also wrote that the study demonstrated increased risk of overall cancer, oral cancer, lung cancer and mesothelioma, and that preventive measures should be researched further.
• Limitations the authors state:
  • There were no personal sampling data, which made dose-response analysis difficult.
  • The only workplace survey (1987, 91 samples) was collected mainly from highly exposed areas, so asbestos levels for other job groups were unclear.
  • Competing causes of death, such as accidents, may mean true cancer incidence was underestimated.
  • The healthy worker effect may have reduced cancer occurrence and led to underestimation of the effect of occupational exposure.
  • There was no information on smoking, alcohol, diet or betel quid chewing, so their influence (for example on oral cancer) could not be assessed.
  • The 24-year follow-up may have been too short to observe mesothelioma, and mesothelioma may be under-estimated or misdiagnosed in Taiwan.
  • Workers who migrated abroad and were diagnosed with cancer would be missed by the Taiwan registry.
  • The authors did not know whether workers changed jobs during their exposure period.

Topics

Medical terms in this study, explained in our Lexicon: Cancer Registry, Standardized Incidence Ratio (SIR), Relative Risk, Hazard Ratio, Latency, Bronchus, Lung Cancer, Mesothelioma.

Related studies

• Cancer Attributable to Asbestos Exposure in Shipbreaking Workers: A Matched-Cohort Study — W.T. Wu, Y.J. Lin, et al. (2015)
• Mortality among shipbreaking workers in Taiwan--a retrospective cohort study from 1985 to 2008 — W.T. Wu, Y.H. Lu, et al. (2013)
• Increased Standardised Incidence Ratio of Malignant Pleural Mesothelioma in Taiwanese Asbestos Workers: A 29-Year Retrospective Cohort Study — C.K. Lin, Y.Y. Chang, et al. (2015)
• Records of the Australian Mesothelioma Surveillance Program have been lost! — M. Hendrickx (2008)
• Cancer incidence among mild steel and stainless steel welders and other metal workers — K.S. Hansen, J.M. Lauritsen, et al. (1996)
• Cancer incidence among asbestos-exposed chemical industry workers: an extended observation period — B. Hilt, A. Andersen, et al. (1991)

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