[Radioiodine-Refractory Differentiated Thyroid Carcinoma in Children and Adolescents: A Retrospective Study]

Differentiated thyroid carcinoma (DTC) in children is a rare malignancy characterized by a high propensity for regional and distant metastases yet generally associated with a favorable long-term prognosis. Radioiodine-refractory (RAIR) disease represents a distinct clinical challenge, accounting for approximately 10-30% of pediatric DTC cases, and warrants comprehensive investigation of its clinical course, prognostic factors, and therapeutic options. This study aimed to perform an integrated assessment of treatment outcomes in children undergoing combined therapy for DTC (surgery and radioiodine therapy, RAI), with a particular focus on advanced and RAIR disease.

We retrospectively analyzed medical records of 278 patients aged 5-18 years who underwent primary surgical treatment between 2008 and 2022, followed by one or more courses of RAI at the Endocrinology Research Centre (Moscow, Russia) from December 2015 to March 2024. The study included patients with advanced disease (high risk of recurrence at diagnosis) fulfilling at least one RAIR criterion, with a median follow-up of 48.0 months [21.5; 62.0].

Among 278 patients, 39 (14%) were diagnosed with advanced disease. Of these, 4 achieved remissions, 29 had stable disease, and 6 experienced biochemical and/or structural progression. Progression-free survival in the RAIR cohort was 85%, while the 5-year overall survival reached 100%.

Based on study findings, we propose a novel classification system integrating both the baseline ability of metastases to accumulate ¹³¹I and the dynamic response to RAI (progression vs. stabilization). This framework is designed to optimize treatment and follow-up algorithms. The management of RAIR pediatric DTC should remain balanced: avoiding overtreatment in stable disease, while ensuring timely initiation of modern systemic therapies in patients with risk factors for progression.