Thyroid Cancer Incidence in North-East Spain, 2002–2021: A Population-Based Study

Background/Objectives: The incidence of thyroid cancer (TC) has increased worldwide over recent decades, particularly for well-differentiated histological subtypes, a trend largely attributed to overdiagnosis. Given potential geographical differences, this study analyzed TC incidence and temporal trends in the province of Girona, Spain, between 2002 and 2021. Methods: We conducted a cross-sectional study using data from the Girona Cancer Registry. Crude incidence rates (CRs), age-standardized incidence rates using the 2013 European (ASRe) and the 1960 World (ASRw) standard populations were calculated per 100,000 person-years. Temporal trends were assessed via the annual percentage change (APC) using generalized linear models. Results: A total of 998 incident TC cases were identified. Most patients were women (78.0%), with a median age at diagnosis of 48 years. Papillary TC was the predominant histological subtype (81.7%), and 70.6% of cases were diagnosed at Stage I. The overall ASRe was 6.8 and ASRw was 5.5, with incidence rates 3–4 times higher in women than in men. Overall, TC incidence increased significantly (APC: 2.7%), driven by increases in the 35–44 and ≥55 age groups, papillary histology, and early-stage disease (Stages I–II). Conclusions: The rise in TC incidence in Girona over the last two decades has been largely driven by Stage I papillary tumors, in both sexes, supporting a potentially substantial contribution of overdiagnosis. However, the concurrent increase in Stage II disease warrants continued surveillance, as it may reflect additional risk factors.