The order of breast cancer lymph node metastasis is related to the location of the breast tumor. If the tumor appears in the upper outer quadrant of the breast, the order of lymph node metastasis is generally to the axillary lymph nodes, then the subclavian lymph nodes, and finally the supraclavicular lymph nodes. If the tumor appears in the inner breast, the order of lymph node metastasis is axillary lymph node, subclavian lymph node, and supraclavicular lymph node, and the tumor may metastasize to the contralateral breast along the sternal lymphatic duct. Once breast cancer has lymph node metastasis, the mammary gland needs to be removed and the lymph nodes need to be completely cleared, both with and without metastatic lymph nodes.