This randomized study compared denosumab, a fully human monoclonal antibody against receptor activator of nuclear factor κ B (RANK) ligand, with zoledronic acid in delaying or preventing skeletal-related events (SREs) in patients with breast cancer with bone metastases.

Patients were randomly assigned to receive either subcutaneous denosumab 120 mg and intravenous placebo (n = 1,026) or intravenous zoledronic acid 4 mg adjusted for creatinine clearance and subcutaneous placebo (n = 1,020) every 4 weeks. All patients were strongly recommended to take daily calcium and vitamin D supplements. The primary end point was time to first on-study SRE (defined as pathologic fracture, radiation or surgery to bone, or spinal cord compression).

Denosumab was superior to zoledronic acid in delaying time to first on-study SRE (hazard ratio, 0.82; 95% CI, 0.71 to 0.95; P = .01 superiority) and time to first and subsequent (multiple) on-study SREs (rate ratio, 0.77; 95% CI, 0.66 to 0.89; P = .001). Reduction in bone turnover markers was greater with denosumab. Overall survival, disease progression, and rates of adverse events (AEs) and serious AEs were similar between groups. An excess of renal AEs and acute-phase reactions occurred with zoledronic acid; hypocalcemia occurred more frequently with denosumab. Osteonecrosis of the jaw occurred infrequently (2.0%, denosumab; 1.4%, zoledronic acid; P = .39).

Denosumab was superior to zoledronic acid in delaying or preventing SREs in patients with breast cancer metastatic to bone and was generally well tolerated. With the convenience of a subcutaneous injection and no requirement for renal monitoring, denosumab represents a potential treatment option for patients with bone metastases.