Inclusion Criteria:
1. Male and female patients aged ≥18 years;
2. 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);
3. Histologically documented TNBC after early breast cancer surgery (absence of HER2, ER, and PR expression)
4. Patients who have undergone standard and adequate surgical treatment;
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. No evidence of metastasis in clinical or imaging examinations before surgery, that is, M0;
7. ECOG score of 0 or 1;
8. Meeting one of the low-risk criteria defined in this study: a) IM subtype, that is, the proportion of stromal tumor-infiltrating lymphocytes is high or CD8 is high; b) LAR subtype and ki-67 less than 20%; c) Age ≥ 70 years.
8)The patient voluntarily joined the study, signed the informed consent form, had good compliance, and cooperated with the follow-up.
Exclusion Criteria:
1. Has received neoadjuvant therapy (include chemotherapy, targeted therapy, radiotherapy or endocrine therapy;
2. Has previous history of additional malignancy, with the exception of adequately treated basal cell carcinoma and cervical carcinoma in situ;
3. Has metastic (Stage 4) breast cancer;
4. Pregnant or breast feeding women, or people of childbearing age who cannot practice effective contraceptives;
5. Patients participating in other clinical trials at the same time;
6. 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; 7) Has a history of psychotropic substance abuse and were unable to abandon drug habits, or those with history of mental disorders; 8)The researchers considered patients to be unsuitable for the study. 9)Has bilateral breast cancer
