Cancer incidence in a cohort of Swedish merchant seafarers between 1985 and 2011

Our plain-English summary of Cancer incidence in a cohort of Swedish merchant seafarers between 1985 and 2011, by K. Forsell, O. Björ, H. Eriksson, et al (International Archives of Occupational and Environmental Health, 2022).

The study

• Authors: K. Forsell, O. Björ, H. Eriksson, B. Järvholm, R. Nilsson, E. Andersson
• Journal: International Archives of Occupational and Environmental Health
• Published: 2022;95(5):1103-1111
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: Lung cancer, mesothelioma and several lifestyle-associated cancer forms have been reported more common in merchant seafarers. However, few studies reflect recent occupational settings and women seafarers are usually too scarce for meaningful analyses. We conducted a study on cancer incidence between 1985 and 2011 in a Swedish cohort consisting of male and female seafarers.

Methods: All seafarers in the Swedish Seafarers' Register with at least one sea service between 1985 and 2011 and a cumulated sea service time of ≥ 30 days (N = 75,745; 64% men, 36% women; 1,245,691 person-years) were linked to the Swedish Cancer Register and followed-up until 31 December 2011. Standardized incidence ratios (SIR) were calculated with the general population as reference.

Results: There were 4159 cancer cases in total, with 3221 among men and 938 among women. Male seafarers had an increased risk of total cancer (SIR 1.05; 95% CI 1.01-1.09), lung cancer (SIR 1.51; 95% CI 1.35-1.67) and urinary bladder cancer (SIR 1.17; 95% CI 1.02-1.33). Several lifestyle-associated cancer forms were more common in men. Previous work on tankers was associated with leukaemia (SIR 1.41; 95% CI 1.00-1.86). The risk of cancer decreased with a start as a male seafarer after 1985, with a significant trend for total cancer (P < 0.001), lung cancer (P = 0.001) and, for tanker seafarers, leukaemia (P = 0.045). Women seafarers had an increased risk of lung cancer (SIR 1.54; 95% CI 1.23-1.87) but the risk of total cancer was not increased (SIR 0.83; 95% CI 0.78-0.89).

Conclusions: In this cohort of merchant Swedish seafarers 1985-2011, the risk of total cancer was increased in men but not in women compared to the general population. Lung cancer was increased in both genders. The risk of cancer seems to decrease over the last decades, but better exposure assessments to occupational carcinogens and longer observation times are needed.

© 2021. The Author(s).

In plain English

This Swedish cohort study linked the Seafarers' Register to the national Cancer Register for 75,745 merchant seafarers (64% men, 36% women) with at least 30 days at sea and service between 1985 and 2011, comparing their cancers with the general Swedish population. Seafarers were grouped by jobs ever held; exposures were not measured. Men had more cancer overall than expected (standardized incidence ratio 1.05; 95% CI 1.01–1.09) and more lung cancer (1.51; 1.35–1.67). All 16 mesotheliomas were in men who first went to sea before 1985; the men's overall mesothelioma ratio, 1.29 (0.73–1.93), was not statistically significant, but men who had ever worked in the engine room had 11 cases against 4 expected (2.59; 1.18–4.23). Women had no mesothelioma, fewer cancers overall than expected (938 observed, 1127 expected) and more lung cancer (1.54; 1.23–1.87). Men who first went to sea later had lower cancer risk, which the authors linked mainly to falling lung cancer. The authors linked the mesotheliomas to asbestos and concluded that seafarers' cancer risks may be becoming more normal, noting short follow-up for later starters.

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 (register-linkage) cohort study comparing cancer incidence with the general Swedish population (standardized incidence ratios)
• Who was studied: 75,745 Swedish merchant seafarers (64% men, 36% women) with at least one sea service between 1985 and 2011 and at least 30 days of cumulative sea service, followed up to 31 December 2011; 1,245,691 person-years
• Exposure: Work at sea, classified by position ever held (deck officer or rating, engine officer or rating, catering/service) and by ever having worked on tankers. Asbestos and other agents were not directly measured.
• Main results:
  • Male seafarers: total cancer SIR 1.05 (95% CI 1.01–1.09), lung cancer SIR 1.51 (95% CI 1.35–1.67), urinary bladder cancer SIR 1.17 (95% CI 1.02–1.33)
  • 16 mesothelioma cases in total, all among seafarers whose first employment was before 1985
  • Pleural mesothelioma (ICD-7 162.2) among all male seafarers: 16 cases, SIR 1.29 (95% CI 0.73–1.93)
  • Among men who had ever worked in the engine room: 11 mesothelioma cases against 4 expected, SIR 2.59 (95% CI 1.18–4.23)
  • The authors interpreted the mesothelioma cases as due to asbestos exposure, noting that most cases had worked in the engine room
  • Male engine room ratings had the highest lung cancer ratio, SIR 1.82 (95% CI 1.49–2.16), described by the authors as almost doubled
  • Among men, cancer risk was lower among those with a later first sea service, a trend the authors attributed mainly to a decline in lung cancer (lung cancer SIR 1.65 for first service before 1985, 1.07 for 1985–1991, 0.76 for 1992 or later; trend P value 0.0014)
  • Women seafarers: fewer cancers than expected overall (938 observed vs. 1127 expected; SIR 0.83, 95% CI 0.78–0.89)
  • Women seafarers: increased lung cancer, SIR 1.54 (95% CI 1.23–1.87), based on 84 cases
  • No mesothelioma cases among women seafarers
  • Men who had worked on tankers: leukaemia SIR 1.41 (95% CI 1.00–1.86)
• The authors' conclusion: The authors concluded that the results lend some support to the view that the earlier increased cancer risks among seafarers are changing to a more normal pattern in modern seafaring.
• Limitations the authors state:
  • The Seafarers' Register lacks seafarers who stopped working before its digitization in 1985
  • The type of cargo was not known
  • Foreign workers were excluded, and cumulative sea service time per seafarer was short
  • No direct information on lifestyle factors; no reliable comparison data on alcohol use
  • No information on other jobs the seafarers held
  • Exposure assessment was crude (based on job category), so exposure may be misclassified
  • Too little follow-up and too few cases to assess cancer risk in seafarers who started later

Topics

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

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

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