The important metastatic pathway of breast cancer is lymph node metastasis. The return of breast lymph nodes includes lateral, medial, contralateral, and downward direction, of which 50%-75% is returned through the lateral breast channel, and the lateral lymph node group, mainly through the axilla, and the return of contralateral lymph nodes can also be transferred to the contralateral axillary lymph nodes through the channel, so attention should be paid to the abnormal enlargement of axillary lymph nodes. Not all enlarged axillary lymph nodes are breast cancer metastasis, most of them are benign reactive hyperplasia. If there is fusion of lymph nodes, unclear structure of lymph nodes, disappearance of lymphatic gates, short diameter of lymph nodes >1cm, etc., then it is considered to be malignant and needs further examination.