7914 Staged Treatment with Radioiodine Following Lobectomy in a Case of High Risk Papillary Thyroid Carcinoma

Abstract Disclosure: L. Pathak: None. A. Sharma: None. K. Rao: None. M.G. Jakoby: None. Introduction: Radioiodine ([1]3[1]I ) is usually reserved for patients with differentiated thyroid carcinoma (DTC) who are at high risk of persistence or recurrence after thyroidectomy. We present a case of papillary thyroid carcinoma (PTC) with extrathyroidal extension managed by lobectomy and staged [1]3[1]I ablation of the contralateral lobe and metastases due to comorbidities that made oncologic resection prohibitive. Case Description: A 58-year-old male had a 2.2 cm focus of PTC in the left thyroid lobe that extended into extrathyroidal soft tissue, adjacent trachea, and completely compromised the left recurrent laryngeal nerve. Due to left vocal cord paralysis and subglottic tracheal stenosis, left lobectomy was performed but oncologic resection (total thyroidectomy and tracheal resection) was deferred. The patient underwent recombinant human TSH (rhTSH) stimulated treatment with 30 mCi (1.1 GBq) of [1]3[1]I for right thyroid lobe ablation followed 60 d later by 180 mCi (6.7 GBq) of [1]3[1]I to treat metastases. Response to treatment was incomplete, with unstimulated thyroglobulin level falling from 293.9 to 18.9 ng/mL 1 y after [1]3[1]I and CT of the neck notable for a 2.7 cm left thyroid bed mass with invasion of adjacent trachea and a 1.0 cm right paratracheal mass, both of which exhibited hypermetabolism on PET imaging and yielded cytology consistent with poorly differentiated thyroid carcinoma (PDTC). A cluster of left supraclavicular lymph nodes showed both hypermetabolism on PET and radioiodine uptake on rhTSH scan. This patient is being prepared for surgical resection of the left thyroid bed and right paratracheal tumors and left lateral lymph node dissection. Discussion: Radioiodine lobar ablation is an alternative to completion thyroidectomy in patients with an unexpected diagnosis of DTC after lobectomy, with a recent meta-analysis finding a success rate of 69%. No difference in thyroid cancer recurrence rates was found in nearly 500 matched pairs of patients undergoing completion thyroidectomy or radioiodine lobar ablation. Unfortunately, staged lobar ablation followed by high dose [1]3[1]I was not successful in treating this high-risk PTC patient. Cases of coexisting PTC and PDTC are reported, and [1]3[1]I treatment was unsuccessful at treating PDTC that was not apparent on postsurgical histopathology. This case indicates that surgery is preferable to staged [1]3[1]I treatment of patients with aggressive PTC, especially if there are no comorbidities that make total thyroidectomy a high-risk procedure. Presentation: 6/2/2024