Dosing interval adjustment of denosumab for the treatment of giant cell tumor of the sphenoid bone: A case report.

BACKGROUND: In the treatment of giant cell tumor of bone (GCTB), the efficacy and safety of denosumab, a receptor activator nuclear factor κ-B ligand inhibitor, has previously been demonstrated, especially for unresectable tumors. One of the current issues in denosumab treatment for unresectable GCTB is whether it can be discontinued, or whether the dosage or the dosing interval can safely be adjusted, if discontinuation is not possible, to avoid the occurrence of side effects. CASE DESCRIPTION: A 15-year-old boy with diplopia was referred to our hospital after a space-occupying lesion in the sphenoid bone was found on head CT. Partial removal of the tumor was performed through an endoscopic endonasal approach, and pathological diagnosis was confirmed as GCTB. Thereafter, the patient received 120 mg subcutaneous injections of denosumab every 28 days for the first 2 years. Since bone formation was induced and sustained along with tumor reduction, the dosing interval was gradually extended, with 4 monthly dosing for the next 1 year, followed by 6 monthly dosing for the succeeding 2 years. With the extension of the dosing interval, the ossified tumor has regrown slightly, but within an acceptable range. CONCLUSION: Discontinuation of denosumab treatment for unresectable GCTB was not thought to be possible for the current case due to the nature of the drug, as reported in the literature. Extending the dosing interval up to 6 monthly, as could be done safely in the current case, can be considered a useful and appropriate measure.