Incidence and Survival of Thyroid Cancer in Children, Adolescents, and Young Adults in Denmark: A Nationwide Study from 1980 to 2014

Background: Thyroid cancer constitutes a major and increasing proportion of head and neck cancers in children and adolescents. The purpose of this study was to determine the incidence and survival of thyroid cancer in Danish patients aged 0-24 years from 1980 to 2014. Methods: Patients aged 0-24 years registered with primary thyroid cancer in the Danish Cancer Registry or the Danish Pathology Data Bank during 1980-2014 were included. Crude incidence rates and age-adjusted incidence rates (AAIR) per 100,000, average annual percent change (AAPC), and overall survival (OS) were evaluated in relation to sex, histopathological tumor type, age at diagnosis, and year of diagnosis. Results: A total of 297 thyroid cancer patients (72% female, 72% papillary carcinoma) were identified. The AAIR per 100,000 increased significantly from 0.36 in 1980 to 0.97 in 2014, with an AAPC of 2.9%. There was no significant increase in incidence among children and adolescents (0-17 years). However, among young adults (18-24 years), a significant increase in incidence was observed (AAPC 3.7%). The incidence of thyroid cancer increased with age from 0.05 among infants aged 0 years to 1.73 among young adults aged 24 years. Female patients and papillary carcinoma showed significant increase in incidence (AAPC 3.3% and 3.2%), whereas male patients and other histopathological tumor types showed no change. The 15-year OS was 99%. The lowest 15-year OS was observed among patients with medullary carcinomas at 96%. There was no significant difference in OS between groups based on histopathological tumor type, and there was no significant change in OS over time. Conclusion: In this nationwide study, no change in OS was observed, but a significant increase was seen in the incidence of thyroid cancer among young adults (aged 18-24 years), mainly attributed to an increase among females and patients with papillary carcinoma. No increase in incidence was seen among children and adolescents. These findings demonstrate the excellent prognosis for children and adolescents diagnosed with thyroid cancer.