Measurement of bone mineral density as an efficacy marker in denosumab treatment of giant cell tumour of bone.

Three patients with giant cell tumour of bone (GCTB) in the lower extremity, where the only surgical treatment options were amputation or severe weakening of the bone, were treated with denosumab (D-mab) to strengthen the bone mass in the tumour. In order to quantify changes in bone mineral density (BMD) in the GCTB lesion during D-mab treatment, we did repeated dual-energy X-ray absorptiometry (DXA) scans. The patients underwent operation after 3, 4 and 8 months of D-mab treatment, respectively. The tumours in all three patients responded markedly to D-mab, and up to 50% BMD increase was observed. There was almost no BMD change in the control scans in the hip and spine of the same patients. DXA scans provide no information about local tumour response, but may be of value in evaluation of the time and size of the D-mab response in GCTB, and thereby aid in finding the best timing for surgery.