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.