Cancer incidence among Danish seafarers: a population based cohort study

Our plain-English summary of Cancer incidence among Danish seafarers: a population based cohort study, by L. Kaerlev, J. Hansen, H.L. Hansen, et al (Occupational and Environmental Medicine, 2005).

The study

• Authors: L. Kaerlev, J. Hansen, H.L. Hansen, P.S. Nielsen
• Journal: Occupational and Environmental Medicine
• Published: 2005;62(11):761-5
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: Seafarers aboard oil and chemical tankers may be exposed to many chemicals, including substances like benzene that are known to be carcinogenic. Other seafarers are exposed to engine exhaust, different oil products, and chemicals used aboard and some years ago asbestos was also used extensively in ships. The aim of this study was to study cancer morbidity among Danish seafarers in relation to type of ship and job title.

Methods: A cohort of all Danish seafarers during 1986-1999 (33,340 men; 11,291 women) registered by the Danish Maritime Authority with an employment history was linked with the nationwide Danish Cancer Registry and followed up for cancer until the end of 2002. The number of person years at risk was 517,518. Standardised incidence ratios (SIR) were estimated by use of the corresponding national rates.

Results: The SIR of all cancers combined was higher than expected: 1.26 (95% CI 1.19 to 1.32) for men and 1.07 (95% CI 0.95 to 1.20) for women. This was mainly due to an excess of cancer of the larynx, lung, tongue, mouth, pharynx, oesophagus, pancreas, kidney, urinary bladder, colon, and bone as well as skin melanomas among men (the three latter borderline significantly increased), and an excess of cancer of the lung, rectum, and cervix uteri among women. The differences in risk pattern for lung cancer between the different job categories among men ranged in terms of SIR from 1.2 (95% CI 0.9 to 1.7) (engine officers) to 2.3 (1.6 to 3.3) (engine room crew), and 4.1 (2.1 to 7.4) among maintenance crew. Non-officers had a 1.5 times higher lung cancer risk than officers. No increased occurrence of all lymphatic and haematopoietic malignancies combined was found for employees on tankers, but the number of cases was limited to a total of 7.

Conclusions: Danish seafarers, especially men, face an increased overall cancer risk, in particular a risk for lung cancer and other tobacco associated cancers.

In plain English

This cohort study followed 44,631 seafarers living in Denmark (33,340 men and 11,291 women) who worked on Danish ships between 1986 and 1999. The authors linked seafarer and cancer registries through the end of 2002 and compared cancers with those expected from national rates. Job title and type of ship stood in for exposure. Men had more cancer overall than expected (standardised incidence ratio 1.26, 95% CI 1.19 to 1.32); for women the ratio was 1.07 (0.95 to 1.20). Lung cancer was raised in both sexes. Among men it was higher in non-officers than officers, and highest in maintenance crew (ratio 4.1, 95% CI 2.1 to 7.4, from 11 cases). Pleural cancer, which here included mesothelioma, was not increased: six cases among men (0.99, 0.36 to 2.16) and none among women. No job group, including engine room personnel, showed increased mesothelioma risk. The authors suggested the young cohort and the 1975 asbestos ban in new Danish ships might explain this. They had no smoking data. They concluded the excess was mainly in lung and other tobacco-associated cancers.

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: Historic (retrospective) population-based cohort study linking the Danish Seafarer Registry with the Danish Cancer Registry; cancer counts compared with national rates as standardised incidence ratios (SIRs)
• Who was studied: All seafarers with permanent residence in Denmark employed on Danish ships 1986–1999: 33,340 men and 11,291 women, followed for cancer until the end of 2002 (517,518 person years)
• Exposure: Seafaring work, classified by most recent job title and by type of ship of longest employment. Asbestos and PAH exposure were considered only through jobs with possible exposure; no individual exposure measurements are reported
• Main results:
  • All cancers combined: SIR 1.26 (95% CI 1.19 to 1.32) for men and 1.07 (95% CI 0.95 to 1.20) for women
  • Lung cancer: men 259 cases, SIR 1.61 (95% CI 1.42 to 1.82); women 29 cases, SIR 1.70 (95% CI 1.14 to 2.44)
  • Lung cancer SIR among men by latest job: engine room crew 2.3 (1.6 to 3.3); maintenance crew 4.1 (2.1 to 7.4), based on 11 cases
  • Lung cancer SIR among men was lower for officers, 1.2 (95% CI 1.1 to 1.5), than for non-officers, 2.1 (95% CI 1.8 to 2.5)
  • Pleural cancer, including mesothelioma: men 6 cases, SIR 0.99 (95% CI 0.36 to 2.16); women 0 cases
  • No increased risk of mesothelioma was found in any job category, including engine room personnel. The authors suggested this could be due to the relatively young cohort and the 1975 ban of asbestos in new Danish ships
  • Tobacco smoking associated cancers: SIR 1.6 (95% CI 1.5 to 1.7) for men and 1.5 (95% CI 1.2 to 1.9) for women
  • No increase in lymphatic and haematopoietic cancers among men whose longest employment was on tankers; only 7 cases
• The authors' conclusion: The authors concluded that Danish seafarers, especially men, face an increased overall cancer risk, in particular for lung cancer and other tobacco-associated cancers
• Limitations the authors state:
  • No information on individual smoking habits
  • Relatively young cohort
  • High turnover suggesting short exposures, and short follow-up of at most 17 years
  • Seafarers without Danish residence (33%) were excluded; the authors noted these were mainly deck and engine room crew, so cancer risk from exposures may be underestimated
  • Using the most recent job title may misclassify exposure for seafarers who were promoted

Topics

The National Library of Medicine indexes this study under subjects our site covers: The Navy.

Medical terms in this study, explained in our Lexicon: Cohort Study, Carcinogenic, Cancer Registry, Standardized Incidence Ratio (SIR), Laryngeal Cancer, Lung Cancer.

Related studies

• Cancer incidence among seafarers and fishermen in the Nordic countries — K. Ugelvig Petersen, E. Pukkala, et al. (2020)
• Cancer at sea: a case-control study among male Finnish seafarers — H. Saarni, J. Pentti, et al. (2002)
• Risk of cancer among Danish utility workers--a nationwide cohort study — C. Johansen, J.H. Olsen (1998)
• Asbestos exposure and haematological malignancies: a Danish cohort study — E.T. Würtz, J. Hansen, et al. (2020)
• Tuberculosis and risk of cancer: a Danish nationwide cohort study — D.F. Simonsen, D.K. Farkas, et al. (2014)
• Asbestos-related cancers among 28,300 military servicemen in the Royal Norwegian Navy — L.A. Strand, J.I. Martinsen, et al. (2010)

Browse more research in Occupational and Environmental Medicine, or return to medical research.