Denosumab induction and Zoledronic acid maintenance therapy for recurrent unresectable giant cell tumour of the distal tibia: A case report with sustained tumour control after drug withdrawal.

A 31-year-old woman was diagnosed with a recurrent and rapidly growing giant cell tumour of distal tibia with skin ulceration after intralesional curettage. The patient started on Denosumab 120 mg subcutaneously, once per month with additional loading doses on Days 8 and 15 attempting to avoid below-knee amputation. Twelve doses of Denosumab were administered in 9 months, resulting in resolution of pain, reduction of tumour size and calcification. Hence, the local surgical treatment was delayed and bisphosphonate maintenance therapy was initiated as skin healing was incomplete. The patient was given Zoledronic acid infusions at a dose of 4 mg. After the third infusion, the skin healed. As tumour remained stable, it was decided to continue maintenance. Overall, six doses of Zoledronic acid at 6 months intervals were administrated over 3 years. At the end of the maintenance, the patient experienced no pain and satisfied with her limb function. Since the lesion remained stable over 3 years after Denosumab discontinuation, it was suggested to stop further medical treatment and proceed to active surveillance. The patient's disease is still stable clinical remission with no serious adverse events 41 months after Denosumab cessation and 10 months after the last bisphosphonate infusion. The present case confirmed the high effectiveness of denosumab as induction therapy in advanced recurrent giant cell tumour. We speculate that following the Denosumab-induced tumour ossification, high Zoledronic acid uptake in lesion may prevent tumour reactivation due to its improved pharmacodynamics with an assumed irreversible anti-tumoral effect on residual mutated cells. This hypothesis requires confirmation in future studies.