Stage I HER2 Positive Invasive Breast Cancer De-escalation Study(IRIS)

Inclusion Criteria: * Females 18-70 years old; * Pathological confirmed of stage I breast cancer: histologically confirmed that the longest diameter of invasive cancer is no more than 2cm and the lymph node is negative (N0); * In IRIS-A cohort, if a patient is HR negative(ER/PR\<10%), the longest diameter of invasive cancer could not exceed 2cm; while if a patient is HR positive(ER and/or PR ≥10%）,the longest diameter of invasive cancer is greater than 1cm and no more than 2cm; * In IRIS-B cohort, a patient need to be HR positive (ER and / or PR expression ≥10%) and the longest diameter of invasive cancer could not exceed 1cm; * The pathological type of immunohistochemistry must meet the following conditions: HER-2 (3+) or HER-2 (0-2 +) with FISH detection is amplified; * For patients with invasive lesions on both sides, if both lesions are HER-2 positive and meet the tumor size requirements, then can be enrolled; * 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); * LVEF\>50%; * The patient voluntarily joined the study, signed the informed consent form, had good compliance, and cooperated with the follow-up. Exclusion Criteria: * Has received neoadjuvant therapy (include chemotherapy, targeted therapy, radiotherapy or endocrine therapy; * Has previous history of additional malignancy, with the exception of adequately treated basal cell carcinoma and cervical carcinoma in situ; * Has metastic (Stage 4) breast cancer; * Pregnant or breast feeding women, or women of childbearing age who cannot practice effective contraceptives; * Patients participating in other clinical trials at the same time; * 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\>150/90mmHg, myocardial infarction, or cerebral blood vessel); diabetic patients with poor blood glucose control; patients with severe hypertension; * Has severe or uncontrolled infection; * Has a history of psychotropic substance abuse and were unable to abandon drug habits, or those with history of mental disorders; * The researchers considered patients to be unsuitable for the study.