SUN-922 An Indolent Recurrent Parathyroid Carcinoma - A Case Report

Introduction Parathyroid carcinoma is a rare endocrine malignancy with reported incidence from 0.5 to 5% of primary hyperparathyroidism (1). Etiologies include prior neck irradiation, adenoma or hyperplastic parathyroid gland. Molecular pathogenesis includes RB gene overexpression, low P53, loss of APC and especially HRPT2 tumor suppressor gene. It has low malignant potential, but tends to recur locally or spread to contiguous areas. Here, we present a case of a recurrent parathyroid carcinoma that recurred after 17 years. Clinical Case The patient is a 56 YO female with Stage 1 breast cancer status post bilateral mastectomy who had underwent resection of a 2.5cm low-grade left lower parathyroid carcinoma in 1997 after 10 years of primary hyperparathyroidism. At that time of resection, iPTH was 2500 pg/ml and calcium level greater than 15 mg/dl. She presented with hypercalcemia (Calcium 11.5 mg/dl, PTH 67.1 pg/ml) again after 17 years. Work-up showed a 2.3 cm suspected parathyroid lesion in the left neck. She underwent removal of the left upper parathyroid gland along with a right enlarged parathyroid gland, as intra-operative PTH did not decline. Pathology confirmed parathyroid carcinoma with capsular invasion and muscle infiltration of the left gland and adenoma of the right gland. Repeat imaging in a month showed persistent parathyroid activity in the left neck. She had removal of the left upper parathyroid and a left paratracheal mass excision with pathology confirming recurrent parathyroid carcinoma. After 4 years, her PTH and calcium levels rose. Sestamibi imaging showed abnormal activity in a 1.1 cm soft tissue mass near the sternal notch. The patient underwent complete excision of the left suprasternal mass and the left sternohyoid muscle with pathology confirming recurrent parathyroid carcinoma with lympho-vascular and perineural invasion. Follow-up Sestamibi imaging after a month showed no abnormal activity with recent labs of calcium level 10mg/dl and PTH 25 pg/ml. Conclusion Recurrent parathyroid carcinoma remains a challenge. Complete resection of the lesion along with care to avoid capsule rupture to prevent local seeding remains the treatment strategy. The main cause of morbidity and mortality is the sequelae of uncontrolled hypercalcemia rather than tumor burden. Management of hypercalcemia includes hydration, bisphosphonates and cinacalcet. Even though it is not radiosensitive, neck radiation after surgery may be helpful in preventing tumor regrowth. Clinical trials using nivolumab and ipilimumab are being conducted to treat parathyroid carcinoma (2). Reference 1. Givi, B., & Shah, J. P. (2010). Parathyroid carcinoma. Clinical oncology, 22(6), 498–507 2. Long, K. L., & Sippel, R. S. (2018). Current and future treatments for parathyroid carcinoma. International Journal of Endocrine Oncology, 5(01), IJE06