Denosumab in pediatric patients with Fibrous Dysplasia/McCune-Albright Syndrome: a single-center, open-labelled study

Quanshi Ouyang¹Ruizhi Jiajue¹Ruotong Zhou¹Wenting Qi²Xiang Li¹Lijia Cui¹Yue Chi¹Qianqian Pang¹Yiyi Gong¹Wei Liu¹Yan Jiang¹Ou Wang¹Mei Li¹Xiaoping Xing¹Weibo Xia^1*

• ¹Peking Union Medical College Hospital (CAMS), Beijing, China
• ²Chinese Academy of Medical Sciences & Peking Union Medical College Plastic Surgery Hospital and Institute, Shijingshan, China

Abstract Context: 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. Objective: Investigate the efficacy and safety of denosumab in pediatric FD/MAS population. Design: 12-month single-arm study. Setting: Single center study at Peking Union Medical College Hospital. Patients: FD/MAS patients under 18. Interventions: Denosumab 1mg/kg with a maximum dosage of 60mg every 3 months for 12-month follow-up. Main Outcome Measures: FD-related bone pain, bone turnover markers, 99mTc-MDP bone scintigraphy, bone mineral density. Results: 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.