SAT-371 - Renal Cell Carcinoma Metastasis to the Thyroid Nineteen Years after Nephrectomy: A Case Report

Objective: Metastases to the thyroid gland account for 2% of all thyroid malignancies, with renal cell carcinoma (RCC) being the most frequent primary tumor, responsible for 48% of metastatic thyroid lesions. Metastases to the thyroid often occur many years after initial RCC diagnosis, with reported intervals of 7-8 years from RCC diagnosis and approximately 6.5 years from nephrectomy to detection of thyroid involvement. We report a case of metastatic RCC to the thyroid in a 74-year-old man, presenting nineteen years after nephrectomy for clear cell RCC. This unusual, long disease-free interval underscores the indolent but persistent metastatic potential of RCC.

Clinical

Case: A 74-year-old male smoker was found to have incidental thyroid nodules on chest CT for lung cancer screening. His past medical history was significant for hypertension, hyperlipidemia, benign prostatic hyperplasia, bladder cancer, and RCC. He had a right radical nephrectomy for a pT2 N0 MX Fuhrman grade 3/4, clear cell renal cancer with negative surgical margins nineteen years ago (2005) and Transurethral Resection of Bladder Tumor for bladder cancer. Relevant family history includes a sister with thyroid surgery and a daughter with hypothyroidism, but a negative family history for thyroid cancer.

Thyroid ultrasound revealed two right lobe nodules measuring 2.2 x 2.3 x 2.7 cm with calcifications and a 0.4 x 0.4 cm cystic nodule. There was also a left lobe solid, isoechoic nodule measuring 1.2 x. 1.2 x 1.4 cm. Ultrasound-guided fine-needle aspiration (FNA) of the right 2.2 cm nodule was performed twice with nondiagnostic results due to limited cellular material. A third FNA showed atypia of undetermined significance in the setting of chronic lymphocytic thyroiditis. Due to the continuous nondescriptive results and inability to exclude malignancy, he underwent right thyroidectomy. The histopathology revealed metastatic carcinoma with clear cell features, compatible with RCC, along with angiolymphatic invasion. There was background thyroid follicular nodular disease and lymphocytic thyroiditis present. Two perithyroidal lymph nodes were negative for carcinoma.

Post operatively he was diagnosed with subclinical hypothyroidism and levothyroxine treatment was initiated. Further metastatic work up revealed a right lower lobe lung nodule confirmed to be metastatic RCC on biopsy leading to Stereotactic Body Radiation Therapy. Given the consistent size of the isoechoic left lobe nodules, left thyroidectomy was not necessary.

Conclusion: The thyroid gland is a rare home to metastases. Although metastatic disease to the thyroid is rare, it is clinically relevant. It is particularly important to consider the possibility of metastasis when evaluating thyroid nodules in patients with a history of RCC, as tumor deposits could lie in the thyroid for several years after RCC diagnosis and treatment.

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