Inclusion Criteria:
1. women aged 18-70 years old;
2. T ≤1cm and negative lymph node confirmed by histopathology after early breast cancer surgery
3. HER2 positive confirmed by histopathology after early breast cancer surgery（HER2-positive breast cancer defined as a positive in situ hybridization test or an Immunohistochemistry (IHC) status of 3+. If IHC is 2+, a negative in situ hybridization (Fluorescence in situ hybridization (FISH), Chromogenic in situ hybridization (CISH) , or Silver in situ hybridization (SISH)) test is required by local laboratory testing.)
4. Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1;
5. Has adequate organ function meeting the following criteria: (1) adequate bone marrow function: hemoglobin ≥ 90 g/L (no blood transfusion within 14 days); absolute neutrophil count ≥ 1.5 x 109 /L; platelet count ≥ 100 \* 109 /L; (2)adequate liver and kidney function: Alanine Aminotransferase (ALT) ≤ 3×upper limit of normal (ULN), Aspartate Aminotransferase (AST) ≤ 3×ULN, Total Bilirubin (TBIL)≤ 1.5×ULN, serum creatinine ≤ 1×ULN，and with endogenous creatinine clearance rate of \>50 ml/min (Cockcroft-Gault formula).
6. Participants voluntarily joined the study, has signed informed consent before any trial related activities are conducted, has good compliance and has agreed to follow-up.
Exclusion Criteria:
1. Has received neoadjuvant therapy (include chemotherapy, targeted therapy, radiotherapy or endocrine therapy）;
2. Has bilateral breast cancer;
3. Has previous history of additional malignancy, with the exception of adequately treated basal cell carcinoma and cervical carcinoma in situ.
4. Has metastic (Stage 4) breast cancer;
5. Is pregnant, is breast feeding women, or women of childbearing age who cannot practice effective contraceptives;
6. Patients participating in other clinical trials at the same time;
7. Has severe organ dysfunction (cardiopulmonary liver and kidney) insufficiency, left ventricular ejection fraction (LVEF) \< 50% (cardiac ultrasound); severe cardio cerebral vascular disease within the 6 months previous of randomization (such as unstable angina, chronic heart failure, uncontrolled hypertension with blood pressure\>150/90mmgh, myocardial infarction, or cerebral blood vessel); diabetic patients with poor blood glucose control; patients with severe hypertension;
8. Has severe or uncontrolled infection;
9. Has a history of psychotropic substance abuse and were unable to abandon drug habits, or those with history of mental disorders;
10. the researchers judged patients to be unsuitable for the study.
