Restoration of radioiodine avidity after lenvatinib in NRAS- and TERT promoter-mutant radioiodine-refractory differentiated thyroid cancer: a case report

To our knowledge, clinically meaningful restoration of radioiodine avidity in established radioiodine-refractory differentiated thyroid cancer has not been reported after multikinase inhibitor therapy, despite successful redifferentiation reported with selective kinase inhibitors targeting BRAF, RAS, RET or NTRK. We report a 53-year-old woman with invasive follicular variant papillary thyroid carcinoma and synchronous cervical lymph node, pulmonary and bone metastases who underwent six cycles of radioiodine therapy within 3 years after total thyroidectomy. Initially radioiodine-avid metastases gradually lost radioiodine avidity, as suggested by serial post-radioiodine therapy whole-body scans. Lenvatinib was initiated after 3 years of active surveillance. Restored radioiodine uptake was observed on rhTSH-assisted diagnostic whole-body scan after 9 months of lenvatinib treatment, allowing subsequent salvage radioiodine therapy. Subsequent post-radioiodine therapy whole-body scans showed increased uptake intensity and additional radioiodine-avid bone metastases, with a marked decrease in suppressed thyroglobulin. Reassessment of radioiodine avidity after prolonged multikinase inhibitor treatment warrants clinical consideration to determine the feasibility of salvage radioiodine therapy.