This projective observational study is planned to enroll more than 300 advanced breast cancer patients, who were proved as Her-2 positive using fluorescence in situ hybridization (FISH) and / or immunohistochemistry, and 100 healthy donors as control. Before treatment, the plasma microRNA will be collected and detected by microRNA extraction kit and quantitative polymerase chain reaction (qPCR), respectively. After analyzed their microRNA expression by microRNA predictive model, previously reported by our team, all of enrolled patients will be classified as "probable sensitive group" or "probable resistant group". Herceptin combined with other chemotherapy will be the backbone of salvage treatment and used for at least 3 months; the change of local masses and metastasis lesions after treatment will be documented to evaluate the response. Based on these results, investigator aim to construct a mathematical predictive model by analyzing the correlation of baseline microRNA expression level and the prognosis of patients. And a diagnosis microRNA kit will be planned and manufactured

Inclusion Criteria:

1. The patients signed the written informed consent
2. female patient who is ≥ 18yrs,
3. HER2 positive: immunohistochemistry (+++) or FISH (+)
4. stage IV
5. the patients have no history of chemotherapy ,hormone therapy,radiotherapy or surgery after diagnosis of breast cancer
6. the result of patients' blood tests are as follow: WBC≥3.0×109/L; Plt≥100×109/L;AST/SGOT or ALT/AGPT≤tripple of normal upper limit; Creatinine\

advanced breast cancer patients first diagnosis in Sun Yat-sen Memorial Hospital, Sun Yat-sen University. Informed consent must be obtained for all of the included patients.