SAT204 Parafibromin: Key To The Diagnosis Of Atypical Parathyroid Adenoma In A Patient With Suspected Carcinoma

Disclosure: V. Anunobi: None. K. Fernandez-Lopez: None. C. Clement: None. N. Shah: None. L. Belalcazar: None. Introduction: Parathyroid carcinoma (PTCa), although a rare endocrine malignancy, should be considered in the differential diagnosis of severe parathyroid (PTH)-mediated hypercalcemia. We present the case of a patient in whom clinical presentation suggested a PTCa, but histological analysis with the use of a parafibromin (PF) stain helped identify the patient’s parathyroid mass as an atypical parathyroid adenoma (APTa). PF stain is now in the World Health Organization (WHO) guidelines for the differentiation of PTCa and APTa. Case Presentation: A 71-year-old woman was admitted to the hospital for an incidental finding of hypercalcemia and complaints of fatigue, myalgias, constipation and generalized weakness. On exam, the patient was alert and oriented; she had a palpable right neck nodule. Laboratory testing included serum calcium of 13.9 mg/dL (8.6-10.6mg/dL) and phosphorus of 2.4 mg/dL (2.5-5.0 mg/dL). PTH level was 3,547.4 pg/mL (12-88 pg/mL) and eGFR was 67ml/min/1.73m(2). Patient had undergone a neck ultrasound prior to admission that described a 2.6 cm right thyroid nodule, however fine needle aspiration revealed that the nodule was a parathyroid mass. Further imaging, including a sestamibi nuclear scan and a neck tomography, confirmed the presence of a large right inferior parathyroid adenoma. After correction of hypercalcemia, the patient underwent a right parathyroidectomy and right hemithyroidectomy. Pathology identified a 7.7 g mass, 3 cm. on its greatest diameter. There was no evidence of lymphovascular or perineural invasion, or extension into the parathyroid capsule or thyroid gland. The mass was strongly positive for PF staining in more than 50 % of tumor cells and was categorized as an APTa. Discussion: Differentiating APTa from PTca is challenging. Preserved PF tumor expression in parathyroid tumors makes PTca unlikely and is linked with a low risk of tumor recurrence. Endocrinologists need to be aware of the utility of the PF stain when evaluating patients suspected to have a PTca. The WHO now recommends that a PF stain be included in the pathological evaluation of these tumors. Presentation: Saturday, June 17, 2023