Although there is a certain risk of recurrence of HER2-positive small tumors, the overall prognosis is relatively good. In order to further reduce the toxicity and side effects of treatment and explore the best strategy for adjuvant therapy in patients with HER2-positive stage IA breast cancer, we designed this phase III, randomized, open-label study to evaluate the efficacy and safety of paclitaxel plus trastuzumab and capecitabine versus paclitaxel plus trastuzumab in the adjuvant treatment of patients with HER2-positive, node-negative breast cancer.

Inclusion Criteria:

1. Females aged 18~70;
2. The postoperative pathological stage of early breast cancer is stage IA: the longest diameter of invasive cancer is not more than 2cm and the lymph node is negative: pT1mic-T1cN0M0 (micro-invasion needs to meet multiple foci).
3. Pathological immunohistochemistry must meet the following conditions: HER-2 (3) or HER-2 (0-2) but amplified by FISH or CISH testing.
4. The maximum number of weeks (56 days) from surgery to randomization is not more than 8 weeks (56 days).
5. The function of major organs is normal, that is, the following criteria are met: (1) The criteria for routine blood examination must meet: HB ≥90 g/L (no blood transfusion within 14 days); ANC ≥1.5×109 /L； PLT ≥100×109 /L； (2) Biochemical tests must meet the following standards: TBIL ≤1.5×ULN (upper limit of normal value); ALT and AST ≤3×ULN; Serum Cr ≤1×ULN, endogenous creatinine clearance >50 ml/min (Cockcroft-Gault formula);
6. Cardiac function: ECG was generally normal, QTc < 470 ms, LVEF >50%;
7. The subjects voluntarily joined the study, signed the informed consent form, had good compliance, and cooperated with the follow-up

Exclusion Criteria:

1. Patients who have received neoadjuvant therapy, including chemotherapy, targeted, radiotherapy, or endocrine therapy;
2. History of other malignant tumors in the past, except for cured basal cell carcinoma of the skin and carcinoma in situ of the cervix;
3. metastasis of any site;
4. Pregnant or lactating women, women of childbearing age who cannot use effective contraception;
5. Patients who are also participating in other clinical trials;
6. Severe organ function (heart, lung, liver, kidney) insufficiency, LEVF < 50% (ultrasound), severe cardiovascular and cerebrovascular diseases (such as: unstable angina, chronic heart failure, uncontrolled hypertension >150/90mmgh, myocardial infarction or cerebrovascular accident) within 6 months before enrollment; Diabetic patients with poor glycemic control; Patients with severe hypertension;
7. Severe or uncontrolled infection;
8. Those who have a history of psychotropic drug abuse and cannot be quit or have a history of mental disorder;
9. Patients who are judged by the investigator to be unsuitable to participate in this study.