The swelling of the arm three years after breast cancer surgery may be caused by poor lymphatic reflux in the arm, or it may be caused by breast cancer recurrence, metastasis and subcutaneous fluid accumulation, and patients are advised to actively follow up with the hospital and receive further treatment if necessary. 1. Poor lymphatic reflux in the arm: It is a common complication after radical breast cancer surgery. Although the lymph nodes around the breast and the ipsilateral brachial plexus lymph nodes are cleared together, the local lymphatic tissues are missing, resulting in obstruction of lymphatic fluid return. Patients can increase physical exercise and strength training to accelerate the establishment of lateral branch circulation; 2. Breast cancer recurrence and metastasis: Although breast cancer is a curable cancer in clinical practice, its recurrence rate is relatively high. When breast cancer recurs and has distant metastasis, the cancer tissue occupies the upper limb and compresses the venous return, which can cause arm swelling. At this time, a surgical plan should be made to treat the lesion with radical resection; 3. Subcutaneous fluid: also a postoperative complication of breast cancer, it is common within one year after surgery, and in a few patients, subcutaneous fluid can last for several years, such as appearing in the third year after surgery. It can be treated clinically with diuretics for symptomatic treatment, such as hydrochlorothiazide.