Efficacy and safety of de-escalation of denosumab for giant cell tumor of the bone

We aimed to investigate the efficacy and safety of denosumab de-escalation for giant cell tumors of the bone (GCTB). We retrospectively reviewed the medical records of nine patients with GCTB that were either unresectable or resectable, but not those of candidates for resection, who received de-escalated denosumab treatment at our institution between 2014 and 2021. The denosumab treatment interval was gradually extended to every 8 weeks, 12 weeks, and 24 weeks. We assessed the radiographic changes and clinical symptoms during the course of standard and de-escalated denosumab therapy. Denosumab interval was de-escalated after a median of 12 months of a standard 4-weekly treatment. Imaging showed that a good therapeutic response obtained with the 4-weekly treatment was sustained until the 8-weekly and 12-weekly treatment. According to the MD Anderson criteria, GCTB treated with de-escalated denosumab therapy resulted in a complete response in one patient and a partial response in eight patients, which were obtained with standard treatment. During the 24-weekly treatment, two patients remained stable, while one patient developed local recurrence. The extraskeletal mass reduced significantly with standard treatment, while tumor reduction was sustained during de-escalated treatment. The clinical symptoms significantly improved with standard treatment and remained improved during de-escalated treatment. In conclusion, de-escalated treatment of denosumab has clinical benefit as a maintenance treatment in patients with unresectable GCTB.