to evaluate whether bone marker can provide the valuable predictor of skeletal complications and whether regular assessing of NTX(N-telopeptide of type I collagen) and osteocalcin can be useful in advanced breast cancer patients with bone metastasis receiving zoledronic acid.

to evaluate the efficacy and safety of zoledronic acid by measuring changes in bone turnover markers

• the incidence of skeletal-related events
• time to skeletal-related events
• time to bone metastases progression
• overall survival
• the incidence of each adverse event including osteonecrosis

Inclusion Criteria:

1. Patients with advanced breast cancer with radiographic confirmation of bone metastases (minimum of one bone scan lesion must be confirmed as metastatic on plain radiographs or CT/MR imaging)
2. Men or women aged ≥ 18 years
3. WHO (ECOG) performance status 0-2
4. Women of child-bearing potential must be using a reliable and appropriate method of contraception
5. Urine sample taken and sent to the central laboratory for baseline Ntx analysis
6. Written informed consent.

Exclusion Criteria:

1. Bisphosphonate treatment within the 4 weeks prior to planned first study treatment
2. Abnormal renal function as evidenced by a calculated creatinine clearance < 30 ml/minute
3. Poor venous access
4. Metabolic bone disease
5. Unable to comply with study procedures, especially the reliable collection of urine samples for bone resorption marker measurements
6. Estimated life expectancy of < 6 months
7. Treatment with systemic bone seeking radioisotopes within the 3 months prior to study entry
8. Wide field (hemi-body) radiotherapy within the 3 months prior to study entry
9. Concomitant medication with drugs known to affect bone metabolism
10. Pregnancy or breast-feeding
11. Current active dental problems including infection of the teeth or jawbone (maxilla or mandibular), or a current or prior diagnosis of osteonecrosis of the jaw (ONJ)
12. Recent (within 4 weeks of study entry*) or planned dental or jaw surgery