7744 Diagnosis of Papillary Thyroid Cancer After Radiofrequency Ablation

Abstract Disclosure: I.S. Barton: None. T.S. Tylee: None. N. Zern: None. M.Y. Roth: None. Background: Radiofrequency ablation (RFA) is a procedure used to decrease the size and compressive symptoms due to a large nodule. Current recommendations are for two fine needle aspirations (FNA) prior to RFA to rule out malignancy. The risk of malignancy after two benign FNAs has been shown to be less than 3%[1]. Here we present a case of nodule regrowth 6 months following RFA, with high-grade thyroid cancer found on subsequent surgical pathology despite 2 benign FNAs prior to RFA. Clinical Case: A 31-year-old female first presented with a thyroid nodule in 2019. Initial thyroid ultrasound demonstrated a 5.0 x 4.0 x 5.5 cm TI-RADS 3 nodule in the right isthmus. TSH was 1.5. She had no family history of thyroid disease, thyroid cancer, or history of radiation exposure. She underwent FNA twice separated by 5 months which both showed benign cytology. Due to compressive symptoms, she underwent RFA of the nodule. Her symptoms improved for approximately 6 months, but she then developed recurrent compressive symptoms. Ultrasound completed 13 months post-RFA demonstrated enlargement of the nodule to 6.0 x 5.8 x 4.0 cm with extension into the right lobe. The nodule remained TI-RADS 3 based on ultrasound characteristics. Due to her compressive symptoms, she underwent right hemithyroidectomy and isthmusectomy. Pathology showed a unifocal 6.5cm differentiated high-grade thyroid carcinoma with extensive angioinvasion, tumor necrosis, focal abutting of surgical margin, and 4 negative lymph nodes (pT3aN0a). She underwent completion thyroidectomy which identified a 5mm infiltrative papillary thyroid cancer in the contralateral lobe. She was treated with radioactive iodine for remnant ablation and adjuvant therapy. Conclusion: This case demonstrates the rare outcome of a high-grade thyroid malignancy diagnosed post-RFA, despite two prior benign FNAs. This may be due to sampling error in large thyroid nodules. Given that most nodules that undergo RFA are larger, it is possible two benign FNAs may not rule out malignancy. This is supported by other studies that have found malignancy in up to 19% of nodules that demonstrate regrowth following RFA2. Thus, ongoing ultrasound follow-up after RFA is important to monitor for nodule regrowth and to recognize potential malignancy. References: (1) Orlandi A, et al. Thyroid. 2005. (2) Kim MK, et al. Korean J Radiol. 2023. Presentation: 6/2/2024