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

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.