Efficacy of Zoledronic Acid and Pamidronate in Breast Cancer Patients: A Comparative Analysis of Randomized Phase III Trials

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Abstract
Results of a large, randomized, comparative phase III trial involving 1,130 breast cancer patients demonstrated that 4 mg zoledronic acid and 90 mg pamidronate were equally effective at reducing the occurrence and delaying the onset of skeletal-related events in patients with bone metastases secondary to breast cancer. However, zoledronic acid has demonstrated a treatment advantage over pamidronate with respect to the proportion of patients receiving radiation therapy to bone. Moreover, among patients with at least one osteolytic lesion (N = 352), zoledronic acid achieved a 17% reduction in the proportion of patients with a skeletal-related event compared with pamidronate and significantly prolonged the time to first event. In general, zoledronic acid and pamidronate had comparable effects on time to progression of bone metastases, overall disease progression, pain and analgesia scores, and overall survival. Both zoledronic acid and pamidronate effectively suppressed markers of bone resorption. However, zoledronic acid demonstrated a greater and more sustained suppressive effect. Zoledronic acid (4 mg via 15-minute infusion) also demonstrated a safety profile similar to that of pamidronate (90 mg via 2-hour infusion). In summary, the increased efficacy of zoledronic acid in specific patient subsets and the convenience of a 15-minute infusion suggest that 4 mg zoledronic acid has advantages over 90 mg pamidronate for treatment of bone metastases in patients with breast cancer.