The Efficacy and Safety of Pyrotinib, Trastuzumab Combined With Taxanes in the Treatment of Trastuzumab-treated HER2+ Advanced Breast Cancer (ABC).

Inclusion Criteria:

1. Age: 18-70 years old, female;
2. Pathological examination confirmed HER-2 positive invasive breast cancer; (HER2 positivity is defined as an immunohistochemical (IHC) score of 3+ or in-situ hybridization (ISH) result for HER2 gene amplification in \>10% of immunoreactive cells.

   HER2 positivity needs to be verified by the pathology department of the research center involved in this study)
3. Imaging confirmed recurrent/metastatic breast cancer;
4. Patients who relapsed and metastasized three months after discontinuation of Trastuzumab treatment;
5. Have at least one measurable lesion (according to RECIST 1.1 criteria);
6. ECOG score of 0-2;
7. Expected life span ≥3 months;
8. Normal major organ function;
9. The researcher believes that the participant may benefit;
10. Volunteer to participate in this study, sign informed consent.

Exclusion Criteria:

Patients who meet any of the following criteria are not eligible for participation:

1. Have any confirmed history of drug allergies, or severe allergic reactions to any component of the investigational drug (NCI-CTCAE 5.0 grade \> 3);
2. Patients in advanced stages who have undergone systemic treatment;
3. A history of serious heart diseases such as congestive heart failure, unstable angina, arrhythmia or myocardial infarction;
4. Suffer from serious pulmonary diseases, such as interstitial lung disease or pneumonia, pulmonary fibrosis, acute pulmonary diseases, etc.;
5. Currently suffering from severe liver-related diseases, such as acute hepatitis, explosive hepatitis, coagulation factor synthesis disorder, etc.; Those who are positive for HBV surface antigen or HBV core antibody must have a peripheral blood Hepatitis B virus DNA titer test \< 1×10 \^3 IU/ml in order to participate;
6. Comorbidity or condition that may interfere with their participation in the study, or any serious medical impediment that might affect participant's safety (such as, active or uncontrolled infection, active liver/gallbladder disease requiring antiviral treatment);
7. Other invasive tumors (including second primary breast cancer) that may affect the evaluation of results and adherence to the protocol;
8. Having undergone major surgical procedure or are yet to recover from major internal diseases within the 4 weeks prior to the study;
9. Any circumstance that the researcher considers the participant unfit to participate in the study.