Refractory hypercalcemia due to hyperparathyroidism in a patient with metastatic parathyroid carcinoma

Hypercalcemia caused by parathyroid carcinoma is an extremely rare malignancy, with resulting higher morbidity and mortality, and remains a difficult challenge for clinicians. We herein have demonstrated the case of a 74-year-old woman with metastatic parathyroid carcinoma, complicated with refractory hypercalcemia both at initial presentation and during disease progression. Initially, her calcium level responded poorly to conventional medical treatments such as hydration, loop diuretics, and bisphosphonates; her hypercalcemia was only resolved after en bloc resection of parathyroid tumor as well as metastasectomy. However, her disease progressed and her hypercalcemia showed only a transient response to cinacalcet in the setting of worsening hyperparathyroidism. Ultimately, the addition of denosumab appeared to provide effective and durable treatment benefits.