Selpercatinib-induced Redifferentiation and Enhanced Radioiodine Uptake in Radioiodine-refractory Thyroid Cancer: A Case Report.

A 32-year-old woman with metastatic papillary thyroid carcinoma, confirmed to harbor an NCOA4-RET fusion and progressing to radioiodine-refractory status, was initiated on selpercatinib. Following 10 months of treatment, serial thyroglobulin (Tg) measurements and post-therapeutic 131I scans after recombinant human TSH stimulation were performed. The scans demonstrated restored diffuse radioiodine uptake in previously refractory lung metastases, accompanied by a significant decline in Tg levels. This case illustrates that selpercatinib can induce effective redifferentiation in RET-altered radioiodine-refractory thyroid cancer, enabling successful radioiodine therapy.