Occupational Variation in Thyroid Cancer Incidence in the Nordic Countries

Introduction: Although the rising worldwide incidence of thyroid cancer (TC) has been largely attributed to changes in diagnostic means, the full spectrum of contributing factors remains unknown. We present a comprehensive registry-based study evaluating the impact of occupational background on the risk of TC in the Nordic countries. Methods: Data were from the Nordic Occupational Cancer (NOCCA) study from the Nordic countries from 1961 to 2005. Standardized incidence ratio (SIR) of TC in each occupational category was calculated using national incidence rates as reference. Results: The NOCCA cohort includes 14.9 million people (7.5 million women (50.3%), 7.4 million men (49.7%)). In total, 23,241 TCs were recorded: 16,758 (71.9%) in women and 6483 in men. Increased SIRs were observed in female farmers (SIR 1.19; 95% CI 1.07–1.30) and male fishermen (1.32;1.06–1.62), military personnel (1.29; 0.99–1.66), and clerical workers (1.19; 1.05–1.35). Conclusion: Our results suggest an association between certain occupational backgrounds and TC. These findings may help elucidate new risk factors for TC to enable targeted diagnosis and surveillance of individuals most at risk.