High-grade Thyroid Cancer Diagnosed After Radiofrequency Ablation Therapy With Multiple Benign Biopsies.

Radiofrequency ablation (RFA) reduces the size of symptomatic thyroid nodules. Two benign fine needle aspirations (FNA) prior to RFA are recommended to rule out malignancy. Here we present a case of high-grade thyroid cancer found on subsequent surgical pathology despite 2 benign FNAs prior to RFA. A 31-year-old female presented with 5.5 cm American College of Radiology Thyroid Imaging Reporting and Data System (ACR-TI-RADS) 3 nodule. Her family history and radiation exposure were negative. She opted for RFA and underwent FNA twice, which was benign. Her compressive symptoms recurred in 6 months. Ultrasound 13 months post-RFA demonstrated enlargement of the nodule to 6.0 cm, representing a 26% growth from the original size before therapy. The nodule remained at TI-RADS 3 based on ultrasound. Due to her compressive symptoms, she underwent a right hemithyroidectomy. Pathology showed a 6.5 cm differentiated high-grade thyroid carcinoma with oncocytic features, tumor necrosis, and extensive angioinvasion (pT3aN0a). She underwent completion thyroidectomy followed by radioactive iodine therapy (RAI). She achieved no evidence of disease status with undetectable thyroglobulin 9 months after the RAI. Ongoing follow-up after RFA is important to monitor for nodule regrowth and to recognize potential malignancy.