PSAT211 Low Grade Parathyroid Carcinoma: A Challenging Diagnosis in the Evaluation of Primary Hyperparathyroidism

BACKGROUND: Parathyroid carcinoma often presents with severe symptomatic hypercalcemia, bone and kidney involvement, and PTH > 4x the upper limit of normal. Diagnosis is challenging and requires classic pathologic findings. CASE PRESENTATION: A 34-year-old woman presented with hypercalcemia. She was found to have primary hyperparathyroidism with elevated total calcium (11.8 mg/dL), elevated PTH (352.8 pg/mL), and elevated 24-hour urine calcium (758 mg/24hr). A 99mTc sestamibi scan showed focal uptake in the right inferior thyroid pole. Intraoperatively, there was a lobulated, fibrotic right parathyroid mass sized 3.5×2.5×2.0 cm. Pathology showed low-grade parathyroid carcinoma with lymphovascular invasion, extension into soft tissue, and focal positivity in resection margin. Post-operative PTH was 19.5 pg/mL. One month later, PTH was elevated to 82.0 pg/mL with calcium of 9.1 mg/dL. PET scan did not show metastases. The patient then underwent a right thyroid lobectomy with central compartment lymph node dissection. Pathology showed residual parathyroid carcinoma within the perithyroidal scar tissue but was negative for lymph node involvement. Postoperatively, her PTH was 52.5 pg/mL. Genetic studies showed no mutations in CDC73, MEN1, RET, RB1, and TP53 genes. She underwent external beam radiation treatment. Following radiation, her total calcium and PTH level remained in the normal range with no recurrence on thyroid ultrasound. CLINICAL LESSONS: On ultrasound, parathyroid carcinomas are large, have increased heterogeneity and lobulations, as well as suspicious lymph nodes. Intraoperative suspicion is based on large size, capsular or local tissue invasion, and lymph node metastases. Histologic assessment can be challenging as findings of parenchymal mitoses, trabeculated parenchyma, and thick fibrous bands are also seen with parathyroid adenomas. Local tissue invasion (angiolymphatic, perineural or adjacent structures) or metastases such as lymph nodes seen on pathology are diagnostic of parathyroid carcinoma. PET can be used post-operatively to identify recurrence or metastases. Genetic studies especially for mutations in CDC73 can be helpful in diagnosis as it is the most common cause of syndromic and sporadic parathyroid carcinoma.Resection of the tumor and adjacent tissues is the mainstay of treatment. A regional lymph node dissection should be done if there are suspicious lymph nodes. Neither thyroidectomy, chemotherapy nor radiation has been shown to improve overall survival. Radiation has shown to have some benefit for local recurrence and disease-free survival. Lifelong monitoring of calcium and PTH levels is required, and if elevated, should prompt imaging with thyroid ultrasound and PET scan. Prognosis is generally poor but does improve if there is complete surgical resection on initial diagnosis. Almost all patients experience recurrence within 2-23 years after resection Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.