Cancer incidence among 41 000 Norwegian offshore oil industry workers

Abstract

Background: In 2012, the production of crude oil and natural gas on the Norwegian continental shelf involved over 50 national and international companies on 80 oil fields along the coastline. It has been a challenge to identify historically workers engaged in this scattered and complex activity, emerging since 1970. Cancer incidence in the workforce may be influenced by exposure to crude oil and petroleum components, combustion products, asbestos, silica, and metals. Additionally, platform workers have 12-hour shifts, abundant food, and long leave periods. Two cohorts have been established for cancer studies in offshore workers: one survey-based, and one from a governmental register of employers and employees. Aims: To investigate the degree of overlap between the cohorts, and to combine them in order to provide the most complete and extended follow-up of cancer incidence to date. Methods: Both cohorts counted nearly 27 000 workers, respectively, representing over 41 000 unique individuals. Incident cancers 1999–2009 were identified by linkage to the national Cancer Registry, and expected numbers were calculated from national age- and gender-specific rates. Standardised incidence ratios (SIRs) with 95% confidence intervals (CIs) were derived. Results: Each cohort shared approximately 50% of its members with the other one. The workers were young, on average turning 50 at the end of follow-up. Overall cancer risk was close to expected, with SIRs of 1.03 (95% CI 0.99–1.08) for men and 1.17 (95% CI 1.02–1.34) for women. The female excess mainly involved skin cancers. Comparison with the general population may underestimate the risks in this selected and active workforce. Some potentially occupational risks found in earlier studies were confirmed. Conclusions: The data indicated that both cohorts are fairly representative samples of Norwegian offshore workers. No large excess was found, but the cancer incidence pattern deserves further attention in studies with exposure data and confounder control.