Denosumab in Patients with Fibrous Dysplasia Previously Treated with Bisphosphonates

Context: Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare bone disorder commonly treated with bisphosphonates, but clinical and biochemical responses may be incomplete. Objective: To evaluate the efficacy and tolerability of the receptor activator of nuclear factor-κB ligand inhibitor denosumab in the treatment of patients with FD/MAS refractory to bisphosphonate therapy. Design: Case series. Setting: Academic center of expertise for rare bone diseases. Patients: Data were collected from 12 consecutive patients with FD/MAS with persistent pain and increased biochemical markers of bone turnover (BTMs) after long-term treatment with bisphosphonates (median, 8.8 years) and were treated with subcutaneous denosumab 60 mg at 3- or 6-month intervals with a follow-up for at least 12 months. Main outcome(s): Sustained reduction of BTMs and bone pain. Results: A 60 mg dose of denosumab once every 3 months, but not once every 6 months, induced a sustained reduction of BTMs. After a median treatment period of 15.5 months (range, 12 to 19) serum alkaline phosphatase activity and propeptide of type 1 procollagen levels were respectively reduced from 212 ± 39.4 IU/L to 79 ± 6.0 IU/L (P = 0.004) and from 346.2 ± 111.1 ng/mL to 55.7 ± 16.6 ng/mL (P = 0.023) and normalized in 70% and 75% of patients, respectively. Although not quantitavely measured, 10 patients reported a reduction in bone pain of whom 6 reported complete elimination of pain. Treatment with denosumab was well tolerated. Conclusion: Our results indicate that 60 mg of denosumab every 3 months is a promising, well-tolerated treatment of most patients with FD/MAS refractory to bisphosphonate therapy. These results together with those of previously published case reports provide the necessary background for the design of a larger, controlled study.