SUN-601 Papillary Thyroid-like Carcinoma Of The Kidney

INTRODUCTION: Papillary thyroid carcinoma (PTC) is the most common thyroid malignancy and usually associated with good prognosis. Typical sites for metastases include lymph nodes, lung and bone, while renal metastasis is rare. Here we present a case of primary papillary thyroid-like carcinoma of the kidney. Histologically and immunohistochemically, the tumor closely resembled PTC, but no abnormalities were found in the thyroid or cervical lymph nodes. CASE REPORT: 54-year-old Caucasian male non-smoker with history of GERD, and dyslipidemia was referred to ENT for evaluation of left tonsillar mass. PET CT showed hypermetabolic regions in the left base of tongue and lingual tonsil, and hypodensity in the lower pole of the left kidney. He underwent bilateral palatine tonsillectomy for invasive squamous cell carcinoma followed by adjuvant chemoradiation. MRI of the abdomen confirmed a 1.7cm left lower pole renal mass and he underwent laparoscopic partial nephrectomy. Pathological examination of the renal tumor was suggestive of papillary carcinoma of thyroid origin (immunohistochemical staining positive for TTF-1, PAX-8 and CK7, and negative for thyroglobulin, RCC, CK20 and racemase). Histologically, the tumor displayed nuclear inclusions, nuclear grooves and papillary architecture. RET oncogene amplification further supported the diagnosis of PTC. Neck ultrasound was negative for thyroid nodules or lymphadenopathy, and no residual hypermetabolic disease was seen on follow-up PET CT. Due to concern for metastatic PTC, the patient underwent total thyroidectomy with central lymph node dissection. Pathology showed only benign thyroid with lymphocytic thyroiditis. Post-thyroidectomy whole body scan showed no abnormal radiotracer uptake to suggest residual thyroid or disease. Serum thyroglobulin level remained undetectable with negative anti-TPO antibodies. DISCUSSION: This patient presented with an incidentally discovered renal tumor that histologically and immunohistochemically resembled PTC. Renal metastasis of PTC is very rare, with less than 20 cases reported, yet positive staining for TTF-1 is highly sensitive and specific for thyroid cells. The possible origins of the tumor include metastasis from an occult intra-thyroidal tumor, primary PTC that had undergone spontaneous resolution, or a primary renal tumor with thyroid-like characteristics. To our knowledge this is the second reported case of a primary papillary thyroid-like cancer of kidney.