non-intervention、real world study； Effect of timing and regular treatment of zoledronic acid on the incidence of SREs in breast cancer patients

(1) Main Purpose: To observe the clinical efficacy of zoledronic acid regularly in the prevention of SREs in breast cancer patients with bone metastasis (2) Secondary Objectives:

1. To observe whether zoledronic acid prolonged the time of first SREs in patients with bone metastasis;
2. The clinical efficacy and influencing factors of zoledronic acid in different subgroups were observed by subgroup analysis of population baseline, clinical characteristics (such as different types of breast cancer), past history and complications.
3. To observe the clinical distribution, characteristics, timing and compliance of zoledronic acid administration in Chinese breast cancer patients with first bone metastasis.

Inclusion Criteria:

• 1. Age ≥18 years 2. Histologically confirmed breast cancer 3. Initial diagnosis of bone metastasis by MRI or CT and treatment with zoledronic acid 4. Serum creatinine ≤265mol/L or 3.0mg/dl 5. CrCl ≥ 30 ml/min 6. Serum Ca2+ concentration 2.0-3.0 mmonl/L 7.ECOG score ≤2 Voluntary research, informed consent

Exclusion Criteria:

• 1. Pregnant and lactating women 2. Severe liver insufficiency (ALT and/or AST higher than 3 times the upper limit of normal) 3. Patients with osteoarthritis or other bone related diseases need bone targeted therapy 4. Patients with uncontrolled dental problems or planned jaw surgery

Histologically confirmed breast cancer, Initial diagnosis of bone metastasis