Neck lymph node swelling one year after breast cancer surgery may be due to lymph node metastasis, obstruction of lymphatic reflux, lymph node inflammation and so on. 1. Lymph node metastasis: malignant tumor cells transfer to regional lymph nodes along lymphatic channels and blood vessels, and breast cancer cancer cells invade regional lymph nodes, resulting in enlarged neck lymph nodes. 2. Obstruction of lymphatic reflux: breast cancer surgery damages lymphatic channels, resulting in local lymphatic fluid not being able to enter the circulation, lymphatic reflux is obstructed and lymph enlargement is formed. 3. Lymphadenitis: it may be caused by bacteria invading from skin and mucous membrane, resulting in inflammation of lymph nodes in the drainage area, which is manifested as enlarged and painful lymph nodes. In addition, tumors originating from lymph nodes may also have similar clinical manifestations. If there is swelling of lymph nodes in the neck, one should go to the hospital for examination in a timely manner to clarify the cause of the disease, so as to avoid delay in treatment.