MON-460 An Extremely Rare Case of Urothelial Carcinoma Metastasizing to the Thyroid Gland

BACKGROUND Metastasis of primary malignancies to the thyroid gland is uncommon, with an overall incidence of 2%. The most common malignancy to metastasize to the thyroid is lung neoplasm (22%) as reported in an autopsy series and renal cell carcinoma (25%) in a clinical series. CLINICAL CASE A 78 year-old-white male was found to have a thyroid nodule on CT neck performed for surveillance of urothelial carcinoma diagnosed 3 years prior. On retrospective review of CT chest from the previous year, the thyroid nodule had increased in size but didn’t meet criteria for FNAC. Neck/Thyroid US demonstrated a right lobe solid hypoechoic nodule measuring 1.1 x 0.7 x 1.1 cm (longitudinal x anterior-posterior, lateral respectively). Nodule margin was well defined, with no internal vascularity, microcalcifications or abnormal cervical lymph nodes. Seven months later, US reported the nodule to have increased in size to 2.1 x 2.1 x 4.7 cm at which point FNAC was performed. Cytology revealed malignant cells compatible with metastasis from the urothelial carcinoma. Three years prior, his high-grade papillary urothelial carcinoma with extensive infiltration into the muscularis propria had been treated with a partial cystectomy and radiation therapy. Surgical margins and all tested lymph nodes had been negative for neoplasm. The patient underwent right thyroid lobectomy and pathology confirmed high-grade malignant neoplasm consistent with metastatic tumor from the patient’s known urothelial carcinoma. CONCLUSION We present a rare case of urothelial carcinoma with metastasis to the thyroid gland. While evaluating thyroid nodules in patients with other known malignancies, clinicians should have a lower threshold for FNAC. This will assist with earlier diagnosis of potential metastatic disease and improve clinical outcomes.