10559 Background: Zoledronic acid reduces the levels of bone markers and the risk of skeletal complications in patients with bone metastases. Recently, a correlation between the levels of biochemical markers of bone metabolism and the risk of clinical complications (ie, skeletal complications, disease progression, and death) in patients with bone metastases has been reported. The effect of zoledronic acid on bone marker levels was assessed in patients with bone metastases from breast cancer in a multicenter randomized trial conducted in Japan. Methods: Women with bone metastases secondary to breast cancer (N = 228) were randomized to 4 mg zoledronic acid (n = 114) or placebo (n = 114) every 4 weeks for 1 year. Levels of urinary N-telopeptide (NTX), a sensitive marker of bone resorption, were measured at baseline and regularly throughout the study. Results: The table shows that zoledronic acid reduced NTX levels in patients compared with placebo. Patients treated with zoledronic acid had a mean decrease of 61% from baseline NTX levels at week 2. This decrease was maintained throughout the study in this treatment group and was 54% at week 52. In contrast, patients in the placebo group had a mean increase of 27% from baseline NTX levels at week 2, and levels of NTX continued to increase during the study, reaching 146% above baseline at week 52. Conclusions: This analysis shows that treatment with zoledronic acid reduced NTX levels in patients with bone metastases from breast cancer compared with placebo. These results are consistent with published reports in patients with prostate or lung cancer and are consistent with the significant reduction in skeletal morbidity observed in this trial in breast cancer patients. Zoledronic acid demonstrated a 39% reduction in skeletal morbidity in this patient population. [Table: see text] No significant financial relationships to disclose.