Significant Response to Denosumab Yet with Severe Rebound Hypercalcemia in a 9-Year-Old Boy with Aneurysmal Bone Cyst: A Case Report

A 9-year-old boy presented with edema of the left cheek. He was diagnosed with a large aneurysmal bone cyst of the mandibular bone. Off-label treatment with denosumab for 17 months resulted in a significant reduction in the lesion. Five months after discontinuing denosumab, the patient developed severe rebound hypercalcemia and acute kidney injury, which resolved with corticosteroids. Two years after treatment discontinuation, the lesion continues to decrease in size. This case highlights the efficacy of denosumab as an off-label treatment for aneurysmal bone cysts, though it can be associated with hypercalcemia and acute kidney injury. We conclude that the use of denosumab should be considered on a case-by-case basis, with regular monitoring for side effects.