Breast cancer stage I, II, III and IV are staged according to the size of primary tumor, lymph node metastasis and distant metastasis. Breast cancer is a common malignant tumor, and in order to guide the treatment and judge the prognosis, TNM staging is often carried out, i.e. staging according to the development of the primary tumor, the degree of lymph node metastasis, and whether distant metastasis occurs. It can be divided into four stages, in which the later the stage, the more complicated the condition and the worse the prognosis. T0: primary cancer not detected Tis: carcinoma in situ T1: tumor diameter ≤2cm T2: tumor diameter >2cm, ≤5cm T3: tumor length and diameter >5cm T4: tumor invades chest wall or skin regardless of tumor size N0: no enlarged lymph nodes in the ipsilateral axilla N1: 1-3 lymph nodes metastasized in the ipsilateral axilla. N2: ≥4 lymph nodes in the ipsilateral armpit N3: ≥10 lymph nodes in the ipsilateral axilla or ipsilateral internal mammary lymph node metastasis M0: no distant metastasis M1: distant metastasis The combination of the three constitutes the staging of breast cancer, which is as follows: Stage 0: TisN0M0 Stage I: T1N0M0 Stage IIa: T0N1M0, T1N1M0, T2N0M0 Stage IIb: T2N1M0, T3N0M0 Stage IIIa: T0N2M0, T1N2M0, T2N2M0, T3N1M0, T3N2M0 Stage IIIb: T4N0M0, T4N1M0, T4N2M0 Stage IIIc: any T, N3M0 Stage IV: any T, any N, M1 Early-stage breast cancer usually refers to stage 0, stage I, stage IIa, stage IIb; stage IIIa, stage IIIb, stage IIIc are usually called locally advanced stage; stage IV is really advanced stage.