Left breast sentinel lymph node is the area that must pass through the lymphatic drainage area of the left breast, which is the first station of tumor metastasis, and the examination of the corresponding area plays an important role in surgical guidance. In the process of metastasis of left breast cancer through lymphatic drainage, there are some areas that must pass through, and the lymph nodes in the first station of the corresponding area become sentinel lymph nodes. Sentinel lymph node is the first station of metastasis. If there is no metastasis in the corresponding area during breast cancer surgery, it is not necessary to do axillary clearance; if there are multiple lymph nodes metastasis, it is necessary to clear the axilla. Once multiple metastasis of sentinel lymph nodes is found in clinic, it is necessary to expand the clearance of surgery in time, and some of them need to be controlled by postoperative adjuvant radiotherapy to control the development of the disease as much as possible to avoid the delay of the disease. If there is any discomfort, it is recommended to go to a regular hospital in time to avoid delaying the condition.