The incidence of thyroid cancer in Danish children, adolescents and young adults.

INTRODUCTION: Previous Danish data (1980-2014) showed a significant increase in thyroid cancer incidence among children and adolescents. This study examined whether this trend persisted during the most recent decade. METHODS: All patients aged 0-24 years diagnosed with thyroid cancer in Denmark between 2015 and 2024 were identified in the Danish Cancer Registry. Crude and age-specific incidence rates (IRs) per 100,000 were calculated for children/adolescents (0-17 years) and young adults (18-24 years), stratified by sex and histological subtype. Trends were analysed using Joinpoint regression. RESULTS: A total of 159 cases were identified; 81% were female. Median age at diagnosis was 16 years in the 0-17-year group and 22 years in the 18-24-year group. Papillary carcinoma was the most common subtype in both groups (68% and 82%). From 2015 to 2024, overall IRs increased non-significantly from 0.65 to 0.94 per 100,000. Across 1980-2024, the incidence increased significantly in young adults (average annual percentage change (AAPC) = 3.4%) and in the total population (AAPC = 2.8%), but not in children/adolescents. IRs increased with age, reaching 4.89 among 24-year-old females and 1.01 among males. CONCLUSIONS: The incidence of thyroid carcinoma in Danish children and young adults has remained stable during the 2015-2024 period, with persistent female predominance and papillary carcinoma as the dominant subtype. Long-term trends continue to show an increasing incidence overall, mainly driven by an increasing incidence among young adults. FUNDING: None. TRIAL REGISTRATION: Not relevant.