SUN-340 A Unique Case of Metastatic Thyroid Cancer without Thyroid Gland Involvement

Abstract Disclosure: K.E. Elkins: None. B.M. DeMoranville: None. Background: Thyroid cancer makes up to 5% of cancers globally. Papillary thyroid carcinoma accounts for up to 80% of all thyroid cancers. Local lymph node metastasis is common among the well differentiated types of thyroid cancer. Occult thyroid carcinoma is a well defined occurrence in which lymph node metastasis is found in the absence of detectable primary tumor via imaging modalities. In such cases, thyroid carcinoma is confirmed via pathological analysis. It is rare to discover occult papillary thyroid carcinoma with pathologically confirmed absence of a primary tumor within the thyroid gland, with only one other case reported in the literature. Case: This is a 63-year-old female without history of thyroid disease who presented with neck discomfort and vision changes. CT angiography (CTA) of head and neck revealed extensive left sided cervical lymphadenopathy with a suspicious node measuring 1.1cm. Neck ultrasonography demonstrated two suspicious left lateral compartment lymph nodes with calcification and abnormal echogenicity. No thyroid lesions or nodules were seen. Fine-needle aspiration of the lymph nodes was positive for Thyroid Transcription Factor 1 (TTF1), thyroglobulin, and paired box gene-8 (PAX-8), consistent with metastatic papillary thyroid cancer. Thyroid function tests were normal. Total thyroidectomy with an extensive left lateral neck dissection was performed. Pathological analysis revealed two out of five level IV lymph nodes and three out of fifteen level III lymph nodes positive for papillary thyroid carcinoma. No papillary carcinoma cells were seen within the thyroid gland itself. Nuclear medicine scans revealed no signs of distant metastases or ectopic foci of malignancy. The patient received high dose radioactive iodine-131 ablation therapy and was started on thyroid hormone replacement therapy. Discussion: In the past, prevalence rates of occult thyroid carcinoma were 2.2%. In the past 10-15 years, this prevalence has dropped to 0.2% with the advancement of ultrasonography. In this case, despite significant lymph node metastases, there was no evidence of primary or ectopic tumor on imaging and no pathological evidence of a primary thyroid cancer. This suggests a highly aggressive microscopic primary tumor with very early metastasis. Thyroid cancer is not rare. It represented 2.2% of all newly diagnosed cancers in 2024. Thyroid cancer is highly curable with a reported 5-year survival rate of 98.4% due to early discovery of most cancerous nodules. This is a case where thyroid cancer presented with lymph node metastases without evidence of thyroid gland involvement. This is a unique presentation of thyroid cancer that may represent a rare subtype of aggressive papillary thyroid carcinoma. Presentation: Sunday, July 13, 2025