Sustained Response with Dose-reduced Selpercatinib in a Pediatric Patient with Metastatic NCOA4-RET Fusion Papillary Thyroid Carcinoma.

Understanding the molecular landscape of papillary thyroid carcinoma (PTC), the most common thyroid cancer in children, creates additional therapeutic approaches. RET gene rearrangements are observed in pediatric PTC, and selective inhibition of RET is now possible with specific tyrosine kinase inhibitors designed to target diverse RET -activating alterations. We present a 13-year-old female with metastatic PTC, clinically resistant to radioactive iodine, and found to harbor a NCOA4-RET fusion. She responded to selpercatinib treatment with the elimination of supplemental oxygen need, marked reduction in pulmonary nodules and mediastinal lymphadenopathy, and biomarker decline. The response was maintained despite 2 dose reductions for possibly related weight gain.