Inclusion Criteria:

          1. Female patients aged ≥ 18 years and ≤ 75 years;

          2. ECOG score 0-1;

          3. HER2-overexpressing breast cancer confirmed by immunohistochemical (IHC) analysis or
             in situ hybridization (ISH).

          4. The patient has received at least 3 cycles of neoadjuvant therapy with trastuzumab
             combined with pertuzumab and the clinical response is SD or PD (according to RECIST
             version 1.1) evaluated with breast MRI/CT/ultrasound.

          5. Known hormone receptor status (ER and PgR);

          6. The function of the main organs must meet the following requirements： 1) Blood
             routine: Neutrophil (ANC) ≥1.5 × 10^9 / L; Platelet count (PLT) ≥90 × 10^9 / L;
             Hemoglobin (Hb) ≥90 g / L; 2) Blood biochemistry: Total bilirubin (TBIL) ≤ upper limit
             of normal value (ULN); Alanine aminotransferase (ALT) and aspartate aminotransferase
             (AST) ≤ 1.5 × ULN; Alkaline phosphatase ≤ 2.5 × ULN; Urea nitrogen (BUN) and
             creatinine (Cr) ≤ 1.5 × ULN; 3) Cardiac ultrasound: Left ventricular ejection fraction
             (LVEF) ≥55%; 4) 12-leads ECG: The QT interval corrected by Fridericia method (QTcF) is
             less than 470 msec.

          7. Voluntarily join the study and sign informed consent, with good compliance and willing
             to cooperate with follow-up.

        Exclusion Criteria:

          1. Stage IV (metastatic) breast cancer;

          2. Inflammatory breast cancer;

          3. There have been other malignant tumors in the past;

          4. Have received anthracycline, cyclophosphamide, or anti-HER2 targeted therapy other
             than trastuzumab/pertuzumab;

          5. Have participated in other clinical trials at the same time;

          6. Have undergone major surgical procedures not related to breast cancer within 4 weeks
             prior to randomization or have not fully recovered from such surgical procedures;

          7. Severe heart disease or discomfort, including but not limited to the following:

             History of diagnosis of heart failure or systolic dysfunction (LVEF <50%); High-risk
             uncontrolled arrhythmias, such as atrial tachycardia, resting heart rate> 100 bpm,
             significant ventricular arrhythmias (such as ventricular tachycardia) or higher-level
             atrioventricular block; Angina pectoris requiring antianginal medication; Clinically
             significant heart valve disease; ECG shows transmural myocardial infarction; Poor
             hypertension control (systolic blood pressure> 180 mmHg and / or diastolic blood
             pressure> 100 mmHg);

          8. Inability to swallow, intestinal obstruction, or other factors that affect medication
             administration and absorption;

          9. People with a known history of allergies to the drugs of this study; a history of
             immunodeficiency, including a positive HIV test, or other acquired or congenital
             immunodeficiency diseases, or a history of organ transplantation;

         10. Pregnant and lactating female patients, female patients with fertility with baseline
             positive pregnancy test, or patients with fertility who are unwilling to use effective
             contraception during the entire trial and within 7 months after the last medication of
             study;

         11. Suffering from a serious concomitant disease or other comorbid condition that
             interferes with the treatment, or any other condition that the researcher considers
             unsuitable to participate in this study.