SUN-600 Metastatic Clear Cell Renal Cell Carcinoma Involving the Thyroid Presenting as Dysphagia

Introduction Metastases to the thyroid represent 1.4-3% of all malignancies. We report a case of renal cell clear cell carcinoma with metastases involving the thyroid 5 years after left nephrectomy. 35 to 80% of patients with thyroid involvement present with multiorgan metastases. Overall prognosis for these patients is dismal, but thyroid metastasectomy for selected patients may offer good survival rates (30–50%). Clinical case 64-year-old Caucasian female was diagnosed with clear cell renal cell cancer (RCC) in 2012 and underwent left radical nephrectomy. A thyroid nodule was first noted in 2012 on her initial staging scans. This nodule, over time, increased in size. In June 2015, CT scan showed a 2.5 x 1.4 cm right thyroid mass which underwent FNA. The cytology was benign. In April 2017, she developed dysphagia. A CT of the neck revealed increase in size of the heterogeneously enhancing mass arising from the right lobe of the thyroid to 4.7 x 3.9 cm. Thyroid function tests were normal through these years. She underwent isthmusectomy and right subtotal thyroidectomy in July 2017. Final histopathology showed metastatic clear cell renal cell carcinoma (Tumor size: around 4 cm). TTF-1 (thyroid transcription factor 1) immunostain highlighted the thyroid follicular cells while RCC immunostain was focal positive in both tumor cells and follicular cells. Subsequent CT neck showed no evidence of disease progression in the neck. There were no enlarged, enhancing, or necrotic cervical lymph nodes. CT thorax/abdomen/pelvis demonstrated bilateral subcm pulmonary nodules, left adrenal nodule and pancreatic head mass. She was then started on pazopanib 800 mg in August 2017. She is currently on levothyroxine 75 mcg daily and most recent TSH was 3.20 µIU/mL (ref. range 0.45 - 5.33) and free T4 0.98 ng/dL (ref. range 0.70 - 1.70). Conclusion Metastases to the thyroid gland are rare in the clinical setting, with the most common primary tumor to metastasize to the thyroid being RCC. Approximately 20% of these patients have distant metastases at the time of diagnosis and 30% will develop metastases during follow-up. In autopsy series, the most common primary tumor to metastasize to thyroid is lung cancer. Presenting symptoms of thyroid metastasis are mostly similar to those with primary thyroid disease. Changes in thyroid function happen late and are uncommon. Regardless of time elapsed since the initial diagnosis of the primary neoplasm, disease recurrence or metastasis must be in the differential when patients present with new signs/symptoms. Although distant metastases carry an adverse prognosis, thyroid metastases have a better outcome than those elsewhere. In contradistinction to primary thyroid malignancy, metastasis to the thyroid is not sensitive to radioactive iodine. Majority will be treated with palliative intent; but for selected patients, lobectomy or total thyroidectomy may be performed.