Abstract
A 65-year-old male presented to our hospital with a complaint of a left cervical mass. The left supraclavicular lymph node was enlarged, measuring 77 mm, and biopsy results confirmed metastasis of papillary thyroid carcinoma (PTC). The left supraclavicular lymph node extended to the upper mediastinum and invaded the internal jugular and subclavian veins, with suspicion of common carotid and subclavian artery invasion. Surgical resection was deemed infeasible. The Oncomine Dx Target Test system, a gene panel test using a next-generation sequencer, of the metastatic lymph node was positive for RET fusion (CCDC6-RET), and selpercatinib treatment was initiated. After 4 months, the tumor reduced in size, and surgery was performed. The postoperative course was uneventful, with ongoing follow-up. This case is a successful case of neoadjuvant chemotherapy for RET fusion-positive PTC with local regional progression.