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

## TL;DR

A 9-year-old boy with a bone cyst showed significant improvement with denosumab treatment, but later developed severe hypercalcemia and kidney issues after stopping the drug.

## Contribution

This case report highlights the efficacy and risks of off-label denosumab use in treating aneurysmal bone cysts in pediatric patients.

## Key findings

- Denosumab significantly reduced the size of the aneurysmal bone cyst over 17 months.
- Discontinuation of denosumab led to severe rebound hypercalcemia and acute kidney injury.
- The lesion continued to decrease in size two years after treatment discontinuation.

## Abstract

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.