This clinical trial aim to evaluate the efficacy and safety of Pyrotinib in combination with nab-paclitaxel in patients with HER2-positive advanced breast cancer.

Inclusion Criteria:

• 1. Age: 18-70 years old，female; 2. Pathologically confirmed HER2-positive invasive breast cancer by local laboratory with the following requirements: HER2 overexpressed or amplified (immunohistochemistry of 3+ or HER2 gene amplification by in situ hybridization) 3. Imaging examination confirmed recurrent/metastatic breast cancer； 4. Patients must have previous treatment with trastuzumab more than 9 weeks; 5. Untreated for metastatic/metastatic disease (except for endocrinotherapy); 6. Patients with at least one measurable lesions by RECIST version 1.1； 7. Eastern Cooperative Oncology Group (ECOG) performance status 0-2； 8. Life expectancy greater than or equal to 3 months; 9. Participants must have normal organ and marrow function as described below： Absolute neutrophil count≥1.5×109/L; Platelets≥90×109/L; Hemoglobin ≥90g/L； Total bilirubin ≤ 1.5 X institutional upper limit of normal (ULN)； ALT and AST≤2*ULN, but ≤5*ULN with liver metastases; BUN and Cr≤1.5×ULN or creatinine clearance ≥50ml/min Left ventricular ejection fraction (LVEF) ≥ 50% 10. Doctors believe that treatment can bring benefits to patients； 11. Participants were willing to join in this study, and written informed consent.

Exclusion Criteria:

• 1. A variety of factors influencing oral drugs (after resection of the gastrointestinal, unable to swallow, Chronic diarrhea, intestinal obstruction); 2. Patients with other malignant tumors within 5 years (except for skin basal cell carcinoma and cervical carcinoma in situ); 3. History of psychiatric drugs abuse or patients with mental disorders; 4. Pregnant or lactating women; 5. Less than 4 weeks from the last clinical trial 6. The researchers think inappropriate.