P3-16-07: Denosumab in Patients with Breast Cancer and Bone Metastases Previously Treated with Zoledronic Acid or Denosumab: Results from the 2-Year Open-Label Extension Treatment Phase of a Pivotal Phase 3 Study.

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Abstract Background Primary results from a phase 3, randomized, double-blind double-dummy trial showed that compared with zoledronic acid (ZA), denosumab reduced the risk of developing a first on-study SRE by 18% (hazard ratio, 0.82; 95% CI 0.71 to 0.95; P = 0.01), and the risk of multiple SREs by 23% (rate ratio, 0.77; 95% CI 0.66 to 0.89; P = 0.001) in patients with breast cancer and bone metastases. Based on superior efficacy and favorable safety data from the study's primary analysis (Stopeck et al, 2010), all patients who remained on treatment were offered open-label denosumab in a prespecified 2-year extension treatment phase. Materials and Methods: A total of 2046 patients with breast cancer and bone metastasis were randomized to receive either subcutaneous (SC) denosumab 120 mg and intravenous (IV) placebo or IV ZA 4 mg (adjusted for renal function) and SC placebo Q4W in the double-blinded treatment phase. Patients who completed the double-blinded treatment phase were offered open-label denosumab Q4W for up to 2 years from the start of the open-label treatment phase. Patients who did not participate in the open-label treatment were followed for survival every 12 weeks for up to 2 years after their last dose of investigational product in the double-blinded treatment phase. Results: Of the 752 patients who completed the double-blinded treatment phase, 667 (89%) patients entered the open-label treatment phase: 325 (48.7%) initially randomized to the denosumab group (DD) and 342 (51.3%) to the ZA group in the double-blinded treatment phase (ZD). Demographics were comparable between groups. The total median (Q1, Q3) cumulative denosumab exposure (including double-blinded and open-label treatment phases) for DD patients was 19.3 months (9.2, 32.2) (range 0.9−59.8 months). Adverse events (AEs) were comparable between groups (n = 283/318 [89%] for DD patients; n = 303/334 [91%] ZD patients). An additional 20 patients in the DD group and 18 patients in the ZD group reported osteonecrosis of the jaw, resulting in a cumulative incidence of 4.7% for DD patients and 3.5% for ZD patients for the entire study duration of 5 years. Hypocalcemia AEs during the open-label treatment phase were comparable between groups (n = 12 DD; n = 9 ZD). The most common AEs were nausea, fatigue, and back pain. Serious AEs were reported in 126 (39.6%) DD patients and 133 (39.8%) ZD patients. Overall survival was similar between groups over the entire study: median 34.4 months (95% CI 31.5 to 39.3) for DD patients, 34.2 months (95% CI 31.0 to 37.6) for ZD patients. Conclusion: A two-year open-label extension treatment phase confirmed the long-term safety profile of denosumab in these breast cancer patients with bone metastases who continued receiving denosumab for up to 5 years or who switched from ZA to denosumab. No new safety signals were observed with up to 5 years of monthly denosumab therapy. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-16-07.