# Denosumab in pediatric patients with fibrous dysplasia/McCune-Albright syndrome: a single-center, open-labeled study

## TL;DR

Denosumab may help reduce bone pain and lesions in children with fibrous dysplasia/McCune-Albright syndrome, but it can cause side effects like hypercalcemia after treatment stops.

## Contribution

This study evaluates the efficacy and safety of denosumab in a small group of pediatric FD/MAS patients for the first time.

## Key findings

- Denosumab reduced bone pain and lesion activity in pediatric FD/MAS patients.
- Alkaline phosphatase and bone turnover markers significantly decreased during treatment.
- Two out of five patients experienced rebound hypercalcemia after treatment cessation.

## Abstract

Fibrous Dysplasia/McCune-Albright Syndrome (FD/MAS) is a rare skeletal disorder frequently manifesting in childhood, often leading to progressive bone lesions, pain and functional impairment. Denosumab as a monoclonal antibody targeting RANKL has emerged as a potential therapeutic option, while its safety and efficacy in pediatric population remains poorly defined.

Investigate the efficacy and safety of denosumab in pediatric FD/MAS population.

12-month single-arm study.

Single center study at Peking Union Medical College Hospital.

FD/MAS patients under 18.

Denosumab 1mg/kg with a maximum dosage of 60mg every 3 months for 12-month follow-up.

FD-related bone pain, bone turnover markers, 99mTc-MDP bone scintigraphy, bone mineral density.

In 5 pediatric FD/MAS patients treated with denosumab, significant clinical improvements were observed, including alleviation of FD-associated bone pain, reductions in bone turnover markers, and regression of FD lesions. Alkaline phosphatase levels dropped to an average of 41.8% of baseline, accompanied by concurrent reductions in C-terminal telopeptide and type 1 N-terminal pro-peptide levels. Adverse events particularly hypercalcemia following treatment cessation occurred in 2 of the 5 patients, indicating a relatively high incidence of rebound hypercalcemia and highlighting the need for careful monitoring and cautious use of denosumab in pediatric patients.

Denosumab appears to be effective in pediatric FD/MAS patients, however safety concerns remain. Comprehensive pre-treatment evaluation and close monitoring throughout the treatment course are essential. Further prospective studies and randomized controlled trials are needed to determine optimal dosing strategies and establish long-term safety in this population.