1. Definition of low risk Patients with negative postoperative lymph nodes and both of the following characteristics: pT ≤ 2 cm, pathological grade 1, no invasion of tumor peripheral vessels, HER-2 (-), and age ≥ 35 years. Chemotherapy regimen can be selected as CMF x 6 or AC/EC x 4-6 cycles. 2. Definition of moderate risk ①Negative axillary lymph nodes with at least one of the following characteristics: pT > 2 cm, pathological grading of grade 2-3, invasion of tumor peripheral vessels, HER-2 gene overexpression or amplification, and age < 35 years. ② axillary lymph node metastasis 1-3 and HER-2(-). The optional chemotherapy regimens are FAC/FEC×6. 3. Definition of high risk ① axillary lymph node metastasis 1-3 and HER-2 (+); ② axillary lymph node metastasis ≥4. The optional chemotherapy regimens are: AC→T, FEC×3→T×3, TAC×6, and also intensive chemotherapy is available.