Effect of zoledronic acid (Zol) compared with pamidronate (Pam) on disease progression in breast cancer (BC) patients with bone metastases stratified by baseline characteristics

Abstract

678 Background: Zol has been shown to significantly reduce the risk of skeletal complications compared with Pam in BC pts with bone metastases. Zol has also demonstrated antitumor effects in animal models of human BC and significantly delayed bone lesion progression in pts with renal cancer. To assess whether Zol may reduce the risk of overall disease progression compared with Pam, we conducted a retrospective analysis of BC pts enrolled in a large randomized, controlled trial. Methods: Patients treated with Zol or Pam were retrospectively stratified by baseline characteristics, including Brief Pain Inventory (BPI) composite pain score, time from initial cancer diagnosis to development of bone metastases, and duration of cancer. The relative risk of overall disease progression during 25 months on study was analyzed using the Cox proportional hazards model. Results: Median BPI pain score at baseline was 2.75, median time to development of bone metastases was 44 months, and median time with cancer was 58 months for all patients. In the subset of pts with a baseline BPI score ≥ 2.75 (n = 556), treatment with Zol significantly reduced the risk of disease progression by 21% compared with Pam (hazard ratio [HR] = 0.793; P = .018). Similarly, among pts who developed bone metastases < 44 months from initial diagnosis of cancer (n = 564) and pts with cancer for < 58 months (n = 563), treatment with Zol reduced the risk of disease progression by approximately 20% compared with Pam (HR = 0.805; P = .026 and HR = 0.800; P = .023, respectively). Conclusions: Zol significantly reduced the risk of overall disease progression compared to Pam in specific subsets of pts with higher pain scores and shorter time to development of bone metastases. This exploratory analysis suggests that Zol has potential antitumor effects that may reduce the risk of disease progression in this patient population. These results are consistent with published reports and provide the initiative for further investigations with additional clinical studies. [Table: see text]