SUN-327 “The Elusive Recurrence: Biochemically Evident But Radiologically Occult Papillary Thyroid Carcinoma”

Abstract Disclosure: A. Farid: None. D. Carrizo: None. Introduction: Papillary thyroid carcinoma (PTC) is typically indolent, with excellent prognosis following surgery and radioactive iodine (RAI) ablation. However, a subset of patients may demonstrate biochemical evidence of disease—elevated thyroglobulin (Tg)—despite negative imaging. This can present a diagnostic and therapeutic dilemma. Retropharyngeal nodal metastases are a rare but recognized site of recurrence, particularly in patients with extensive nodal disease at initial presentation.¹ Clinical Case: A 78-year-old male was diagnosed with stage T3N1bM0 papillary thyroid carcinoma and underwent bilateral total thyroidectomy with central (level 6) and right lateral neck dissection (levels 2, 3, and 4). Pathology showed focal extrathyroidal extension and nodal metastases in 2 of 11 central and 4 of 41 right lateral lymph nodes. He received adjuvant radioactive iodine (I-131) ablation and was maintained on suppressive levothyroxine therapy. Initial post-treatment thyroglobulin (Tg) levels were low but detectable, plateauing at 6 ng/mL. Upon TSH stimulation for a whole-body scan, Tg increased significantly to 260 ng/mL, though imaging failed to reveal structural recurrence. In light of the biochemical profile, a second empirical RAI ablation was administered. Subsequent CT imaging identified a stable, right retropharyngeal lymph node. Although PET imaging remained negative, follow-up CT months later revealed progressive nodal enlargement. Fine-needle aspiration confirmed metastatic papillary thyroid carcinoma. The node was surgically resected and the patient subsequently received another dose of I-131 resulting in undetectable serum Tg levels. Postoperative surveillance has shown undetectable Tg and anti-Tg antibody levels, with serial neck ultrasounds and whole-body scans remaining unremarkable. The patient remains clinically and radiographically disease-free while continuing thyroid hormone replacement therapy. Conclusion: This case underscores the importance of integrating biochemical markers with imaging and histopathology in the long-term surveillance of differentiated thyroid cancer. A rising stimulated thyroglobulin in the context of negative imaging should prompt a high index of suspicion for occult disease. Retropharyngeal lymph node metastases, although rare, may account for such presentations and require surgical intervention.² Personalized care and multidisciplinary follow-up remain critical in managing elderly patients with recurrent PTC. References: 1. Durante C, Montesano T, Attard M, et al. Long-term surveillance of differentiated thyroid cancer patients with detectable serum thyroglobulin but no structural evidence of disease: a clinical challenge. 2. Sahli ZT, Tartar DM, Silverstein AD, et al. Retropharyngeal lymph node metastases in well-differentiated thyroid carcinoma: a systematic review. Presentation: Sunday, July 13, 2025