['her2 positive metastatic breast cancer']
['pyrotinib', 'placebo', 'capecitabine']

        Inclusion Criteria:

          1. Aged ≥18 and ≤75 years.

          2. ECOG performance status of 0 to 1.

          3. Life expectancy of more than 12 weeks.

          4. According to RECIST 1.1, at least one measurable lesion exists

          5. Histologically or cytologic confirmed HER2 positive advanced breast cancer which
             failed prior therapies.

          6. Prior treatment with trastuzumab(≥2 cycles in the metastatic setting, or ≥3 months in
             adjuvant setting), and the patients are not available for the trastuzumab or lapatinib

          7. Previously reveived both Anthracyclin and Taxane.

          8. Required laboratory values including following parameters:

             ANC: ≥ 1.5 x 10^9/L; Platelet count: ≥ 90 x 10^9/L; Hemoglobin: ≥ 9.0 g/dL; Total
             bilirubin: ≤ 1.5 x upper limit of normal (ULN); ALT and AST: ≤ 2 x ULN(patients with
             liver metastases: </= 5 x ULN); BUN and Creatinine: ≤ 1.5 x ULN;LVEF: ≥ 50%;QTcF: <
             470 ms.

          9. Signed informed consent

        Exclusion Criteria:

          1. Received previous therapy with lapatinib, neratinib, pyrotinib or any other HER2
             directe tyrosine kinase inhibitor.

          2. Received previous therapy with capecitabine.

          3. History of receiving chemotherapy, target-therapy or investigational treatment within
             28 days prior to randomization. Received hormone therapy within 7 days prior to
             randomization.

          4. Brain metastases that are untreated, symptomatic, or require therapy to control
             symptoms.

          5. Current severe, uncontrolled systemic disease.

          6. Unable or unwilling to swallow tablets.
      