Recurrent Metastasized Parathyroid Carcinoma-Long-Term Remission After Combined Treatments With Surgery, Radiotherapy, Cinacalcet, Zoledronic Acid, and Temozolomide.

Parathyroid carcinoma is a rare cause of primary hyperparathyroidism with rather poor prognosis. Apart from surgery, no evidence-based treatments exist. A 48-year-old woman presented with weight loss, nausea, constipation, hypercalcemic crisis, and a recurrent neck tumor 5 years after primary surgery of a parathyroid tumor that primarily was classified as an adenoma. Histopathological reevaluation of the original tumor revealed the correct diagnosis to be parathyroid carcinoma (PC). The patient underwent surgery of the recurrent tumor, which was locally invasive with metastatic spread to the mediastinum and neck lymph nodes. Computed tomography demonstrated large lytic bone lesions in both iliac bones including, on the right, a soft tissue mass compatible with bone metastasis. The patient was treated with cinacalcet, repeated zoledronic acid infusions, and temozolomide cycles for 1 year. She underwent two additional neck surgeries for PC and sternotomy for resection of mediastinal metastases. Massive osteolytic lesions in both femoral necks caused imminent fracture risk and therefore both femurs were prophylactically stabilized by intramedullary nail. Serum calcium normalized after the third neck surgery, cinacalcet was discontinued, and parathyroid hormone gradually normalized during continued treatments with temozolomide, adjuvant radiotherapy, and zoledronic acid, with no signs of active disease on imaging and normal biochemistry. The patient remains in remission 17 years after successful combined treatments for recurrent, metastasized PC. The parathyroid tumor tissue demonstrated high O