Selpercatinib Increases Radioactive Iodine Avidity in <i>RET</i> -Fusion Pediatric Thyroid Carcinoma

Papillary thyroid carcinoma (PTC) is one of the most common cancers in adolescents. The management of patients with advanced, metastatic PTC includes surgery and radioactive iodine (RAI); however, less than 20% of children with pulmonary metastases achieve a complete response to RAI. The discovery of targetable molecular alterations in pediatric PTC, including BRAF V600E mutations as well as RET and NTRK fusions, has broadened our therapeutic approach in pediatric patients with advanced and/or refractory disease. Targeted therapy in advanced thyroid cancer has been shown to resensitize tumors to RAI in adults. We describe 2 adolescents with RET-fusion and noniodine avid metastatic PTC who both achieved increased iodine avidity after treatment with selpercatinib, a selective inhibitor of RET, allowing for the successful use of RAI. These cases highlight the potential to include targeted therapy to optimize the treatment with RAI in pediatric patients with noniodine avid advanced PTC.