Denosumab for craniofacial fibrous dysplasia: duration of efficacy and post-treatment effects.

Denosumab has been advocated as a potential treatment for the rare skeletal disorder fibrous dysplasia (FD); however, there is limited data to support safety and efficacy, particularly after drug discontinuation. We report a case of successful treatment of aggressive craniofacial FD with denosumab, highlighting novel insights into the duration of efficacy, surrogate treatment markers, and discontinuation effects. A 13-year-old girl presented with persistent pain and expansion of a maxillary FD lesion, which was not responsive to repeated surgical procedures or bisphosphonates. Pre-treatment biopsy showed high RANKL expression and localization with proliferation markers. Denosumab therapy was associated with improved pain, decreased bone turnover markers, and increased lesion density on computed tomography scan. During 3.5 years of treatment, the patient developed increased non-lesional bone density, and after denosumab discontinuation, she developed hypercalcemia managed with bisphosphonates. Pain relief and lesion stability continued for 2 years following treatment, and symptom recurrence coincided with increased bone turnover markers and decreased lesion density back to pre-treatment levels. This case highlights the importance of considering the duration of efficacy when treating patients with FD and other nonresectable skeletal neoplasms that require long-term management.