SAT567 Collision Tumor Of The Thyroid With Papillary Thyroid Carcinoma And Metastatic Renal Clear Cell Carcinoma With Concomitant Parathyroid Adenoma

Abstract Disclosure: C.M. Mirano: None. R.C. Mirasol: None. INTRODUCTION Collision tumors of the thyroid are rare diseases that have two or more histologically and morphologically distinct tumors that occur simultaneously within the thyroid. There are only a few reported cases of collision tumors involving a metastasis from a distant tumor and a papillary thyroid cancer. In addition, the coexistence of Primary Hyperparathyroidism (PHPT) with nonmedullary thyroid cancers is unusual with an incidence range between 2 to 24%. Here, we describe an unusual case of a patient with Papillary Thyroid Carcinoma and Metastatic Renal Clear Cell Carcinoma complicated with a Parathyroid Adenoma. CASE The patient is a 65 year-old female, known Renal Clear Cell Carcinoma Stage IV who underwent left nephrectomy, distal pancreatectomy splenectomy, and adjuvant chemotherapy. She then developed subclinical hyperthyroidism with bilateral thyroid nodules on ultrasound 13 years post nephrectomy. Thyroid Scintigraphy showed hypofunctioning nodules on both lobes. Biopsy of the thyroid nodules was done on showing a Metastatic Renal Cell Carcinoma. Laboratory tests also showed hypercalcemia and an elevated iPTH. SPECT-CT images showed uptake in the left thyroid suggestive of a parathyroid adenoma. She underwent four gland exploration with parathyroidectomy. Intraoperatively, pre-excision PTH assay extracted peripherally was 386.10 pg/mL. The right superior, right inferior, and left superior parathyroid gland were normal in size. The left inferior parathyroid gland was found to be enlarged measuring 2.5 x 2.0 cm, intrathyroidal in location and was encapsulated. The left inferior parathyroid was dissected and sent for histopathology. 10 minutes post excision PTH levels declined by 57%. After which, total thyroidectomy was done with note of a 2.5 x 2 cm firm mass at the right thyroid lobe slightly adherent to strap muscles. The left thyroid lobe had no palpable nodules, Histopathology of the thyroid isthmus showed one focus of follicular cells exhibiting nuclear changes consistent with papillary thyroid carcinoma. Microsections of the right thyroid lobe show a malignant neoplasm composed of atypical cells arranged in sheets that have enlarged, hyperchromatic to vesicular, pleomorphic, prominent nucleoli, irregular nuclear border, and clear cytoplasm consistent with metastatic clear cell carcinoma. Histopathology of the Left inferior parathyroid gland revealed findings consistent with Parathyroid Adenoma. She was discharged stable with normal calcium levels. CONCLUSION Collision tumors are rare and an adequate histologic assessment of these tumors are important for decisions regarding management. Differentials with patients with nodular goiter should always include metastatic disease in the background of an underlying carcinoma. It is equally important to be aware of concomitant PHPT and thyroid diseases in the management of patients with hypercalcemia. Presentation: Saturday, June 17, 2023