7159 Brown Tumor As Primary Presentation Of Parathyroid Carcinoma In A Young Female

Abstract Disclosure: S.G. Zachariah: None. R. Anand: None. B.Y. Wong: None. H.J. Lee: None. Title Brown Tumor as Primary Presentation of Parathyroid Carcinoma in a Young Female Introduction/Background: Parathyroid carcinoma (PC) is a rare cause of hyperparathyroidism (HPT) accounting for less than 1% of primary HPT cases. The mean age of PC presentation is 62 years. Long-standing HPT can lead to the formation of osteitis fibrosis cystica (brown tumors). In today’s world of advanced screening, they are an increasingly rare presentation of HPT. We present a case of PC presenting as multiple brown tumors in a young woman. Case: A previously healthy 32-year-old woman presented to the emergency department with right shoulder pain after a mechanical fall. MRI revealed multiple osseous lesions of the proximal humerus, glenoid, and scapula, concerning for possible metastatic malignancy. Notable labs: calcium 13.6 mg/dL [8.5 - 10.5 mg/dL], phosphorus 1.7 mg/dL [2.5 - 4.5 mg/dL], alkaline phosphatase 2,369 U/L [< 130 U/L], 25-OH vitamin D 0.8 ng/mL [30 - 60 ng/mL], and parathyroid hormone greater than 2,500 pg/mL [20-80 pg/mL]. Albumin and renal function were normal. CT chest/abdomen/pelvis showed lytic lesions of the left 7th rib, anterior superior iliac spine (with nondisplaced fracture), pelvis, and sacrum. Subsequent pelvic biopsy showed fragmented bony trabeculae with osteoblastic rimming and rare osteoclasts, fragments of fibrous tissue with few plasma cells and hemosiderin laden macrophages, possibly consistent with brown tumor. On parathyroid ultrasound, a 2.2 cm cystic mass was seen along the left common carotid artery. CT neck confirmed the location and also reported C7-T1 spinal lesions. Calcium levels stabilized with IV fluids and 90 mg IV pamidronate. She underwent a left parathyroidectomy and left hemithyroidectomy with central neck dissection. Pathology was consistent with a low-grade parathyroid carcinoma, with a foci of angioinvasion and capsular invasion without lymph node metastases. The Ki-67 index was less than 1%. Post-operatively, the patient was started on calcium and calcitriol supplementation and did not experience hungry bone syndrome. On further discussion, the patient noted that she had a jaw tumor that was previously biopsied and found to be benign. The patient has since been referred for genetic testing. Conclusion/Clinical Lessons: Both PC and its initial presentation with brown tumors are uncommon. Even more rare is the presentation of both in a young, otherwise healthy female. In this context, it is also important to note that brown tumors can mimic osseous metastases and appropriate biochemical, imaging, and histopathological evaluation is needed. The diagnosis of PC under 40 years of age is uncommon and genetic testing is indicated. Syndromes including multiple endocrine neoplasia type 1, familial isolated hyperparathyroidism, and hyperparathyroidism-jaw tumor syndrome are potential causes of inherited PC. Presentation: 6/3/2024