Early evaluation of the therapeutic effect of denosumab on tartrate-resistant acid phosphatase 5b expression in a giant cell tumor of bone: a case report

BACKGROUND: Giant cell tumor of bone is an osteolytic, usually benign, tumor characterized by the infiltration of osteoclast-like giant cells. The receptor activator of nuclear factor kappa-B ligand pathway has been shown to play a key role in the pathogenesis of giant cell tumor. Treatment for refractory, recurrent, or metastatic giant cell tumor remains challenging. A monoclonal antibody to receptor activator of nuclear factor kappa-B ligand, denosumab, offers promise in these patients. Tartrate-resistant acid phosphatase 5b, a bone resorption marker, is secreted from osteoclasts and this marker is reported to be high in patients with giant cell tumor of bone. We investigated the effects of denosumab and the usefulness of a tartrate-resistant acid phosphatase 5b as a monitoring marker in the management of a refractory giant cell tumor of bone. CASE PRESENTATION: A 41-year-old Japanese male with right ischiac pain was diagnosed with a giant cell tumor in his right ischium. Since the tumor extended to the acetabulum, there was a possibility that en bloc resection might significantly impair function of the hip joint and curettage could cause massive bleeding. Therefore, denosumab therapy (120 mg, administered 3 times every 4 weeks) was performed before radical surgery. The giant cell tumor of bone was treated with denosumab successfully. No adverse reaction was noted. Tartrate-resistant acid phosphatase 5b secretion was measured in the patient's serum to monitor the response to denosumab, and a rapid normalization of the marker was observed after the first denosumab administration. CONCLUSION: This case suggests that denosumab therapy might be an option for treating refractory giant cell tumor of bone, and that tartrate-resistant acid phosphatase 5b might be an early marker with which to monitor the efficacy of denosumab therapy for refractory giant cell tumor.