Cancer Incidence Among Swedish Seafarers Between 1985 and 2020

Our plain-English summary of Cancer Incidence Among Swedish Seafarers Between 1985 and 2020, by M. Wallin, H.P. Eriksson, K. Forsell, et al (American Journal of Industrial Medicine, 2026).

The study

• Authors: M. Wallin, H.P. Eriksson, K. Forsell, E. Andersson
• Journal: American Journal of Industrial Medicine
• Published: 2026;69(11):960-971
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Several studies from different countries have shown that merchant seafarers have an increased cancer risk compared to the general population. The aim of this study was to provide updated information on cancer incidence in a cohort of Swedish seafarers.

Methods: A cohort consisting of all Swedish seafarers from the Swedish Seafarers' Register 1985-2013 was linked to the Swedish Cancer Register 1985-2020. Seafarers with at least 5 years of sea service (N = 38,030; 76% men and 24% women) were included in the analyses. Standardized incidence ratios (SIR) were calculated for cancer by specific site, period of first signing, job category, type of vessel, and gender, using cancer incidence in the general population as reference.

Results: In seafarers who had worked on different types of vessels (not solely passenger ferries), there were 5076 cases of cancer during the follow-up period, and total cancer risk was increased (SIR 1.14; 95% confidence interval [CI] 1.11-1.17). Most cases occurred in seafarers who had their first signing before 1985. The risk of lung cancer was increased in all job categories, especially in engine room crew members (SIR 1.98; 95% CI 1.53-2.57). There were 16 mesothelioma cases in engine officers (SIR 3.75; 95% CI 2.30-6.12).

Conclusions: This cohort study of seafarers in Sweden confirms that Swedish seafarers had an increased overall cancer risk compared with the general population, particularly those signing before 1985 and working on different types of vessels.

© 2026 The Author(s). American Journal of Industrial Medicine published by Wiley Periodicals LLC.

In plain English

This register study followed 38,030 Swedish seafarers (76% men) with at least five years of sea service. The authors linked the Swedish Seafarers' Register (1985 to 2013) with the Swedish Cancer Register (1985 to 2020) and compared cancer rates with the Swedish general population. On different types of vessels (not solely passenger ferries), there were 5076 cancer cases, and overall risk was raised (SIR 1.14; 95% CI 1.11–1.17). Most cases (91%) were in people who first signed on before 1985. In that earlier group, lung cancer was raised in every job category and highest in engine crew (SIR 1.98; 95% CI 1.53–2.57). Among that group's job categories, pleural mesothelioma was significantly raised only in ever engine officers (16 cases; SIR 3.75; 95% CI 2.30–6.12). Ferry-only seafarers were analyzed only if they started in 1985 or later. They had no raised overall risk (SIR 0.93; 95% CI 0.86–1.00), though pleural mesothelioma was raised (four cases; SIR 3.30; 95% CI 1.24–8.80). Asbestos was not measured. The authors suggested engine-room carcinogens such as asbestos could explain part of the lung cancer differences. They concluded that Swedish seafarers still had an increased overall cancer risk.

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: Longitudinal (retrospective, register-based) cohort study comparing cancer incidence with the Swedish general population using standardized incidence ratios (SIR)
• Who was studied: 38,030 Swedish seafarers (76% men, 24% women) from the Swedish Seafarers' Register 1985–2013 with at least five years of sea service, linked to the Swedish Cancer Register 1985–2020
• Exposure: Work as a merchant seafarer, classified by period of first signing (before 1985, or 1985 and later), job category (deck officer, ever engine officer, deck crew, engine crew, solely service) and vessel type (different types of vessels vs solely passenger ferries). Asbestos and other exposures were not measured individually; the authors discuss asbestos in the engine room as a possible explanation.
• Main results:
  • Seafarers who had worked on different types of vessels (not solely passenger ferries): 5076 cancer cases (4647 in men, 429 in women); total cancer risk SIR 1.14 (95% CI 1.11–1.17)
  • 91% of cases were in those who first signed before 1985. After stratifying by gender and period of first signing, total cancer risk was significantly raised only in men signing before 1985 (SIR 1.16, 95% CI 1.12–1.19).
  • All seafarers on different vessels (genders combined): increased risk of cancer of the mouth, pharynx, esophagus, stomach, liver, larynx, lung, pleura, and urinary bladder
  • Seafarers starting before 1985 on different vessels, by job category: mesothelioma was significantly increased only in those who had ever worked as engine officers, with 16 cases (SIR 3.75; 95% CI 2.30–6.12)
  • Seafarers starting before 1985 on different vessels: lung cancer was increased in all job categories, especially engine room crew (SIR 1.98; 95% CI 1.53–2.57)
  • Women signing in 1985 or later, on different vessels: lung cancer significantly increased (SIR 3.47; 95% CI 1.97–6.10), based on 12 cases
  • Seafarers who worked solely on passenger ferries were analyzed only for those whose registered signings started in 1985 or later, because earlier register data were incomplete
  • Seafarers who worked solely on passenger ferries (started 1985–2013): no increased total cancer risk (SIR 0.93; 95% CI 0.86–1.00)
  • Seafarers who worked solely with service on passenger ferries: increased risk of mouth cancer (SIR 2.24; 95% CI 1.30–3.86) and lung cancer (1.43; 95% CI 1.05–1.96)
  • Seafarers who worked solely on passenger ferries (started 1985–2013), all job categories combined: four cases of pleural mesothelioma (SIR 3.30; 95% CI 1.24–8.80)
• The authors' conclusion: The authors concluded that merchant seafarers in Sweden still had an increased overall cancer risk compared with the Swedish general population, particularly those who had worked on different types of vessels. They added that the risk had probably decreased in recent years, though not for all cancer types.
• Limitations the authors state:
  • No individual data on smoking, alcohol consumption or physical exercise
  • Most of the cohort were men, so statistical power for women was limited
  • Possible healthy worker effect, because seafarers need a valid medical certificate
  • Incomplete follow-up of seafarers who started before 1985: only those still working in 1985 were included
  • No reliable data on carcinogenic exposures among seafarers in more recent years

Topics

The National Library of Medicine indexes this study under subjects our site covers: Shipyards and maritime work.

Medical terms in this study, explained in our Lexicon: Standardized Incidence Ratio (SIR), confidence interval, Lung Cancer, Mesothelioma, Cohort Study.

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• Cancer incidence among Danish seafarers: a population based cohort study — L. Kaerlev, J. Hansen, et al. (2005)

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