Redifferentiation of a RET-Fusion, Radioiodine-Refractory, Differentiated Thyroid Cancer with Selpercatinib: Flip-Flop Between [18F]FDG PET/CT and131I Posttreatment Scanning

A 29-y-old woman requiring total thyroidectomy with lymph node dissection for a stage pT3(m)N1bMxR2 solid variant of papillary thyroid cancer had, near the left recurrent vagal nerve, a 16 × 10 × 8 mm cervical tumor residue deemed unresectable by expert surgeons. After hormone withdrawal, she