The reasons for the patient’s activity pain appearing eight months after breast cancer surgery generally include surgical factors such as postoperative lymphedema and other factors such as edema caused by radiotherapy. 1. Surgical factors mainly occur in patients who have undergone axillary lymph node dissection, because axillary lymph nodes are the necessary route for lymphatic return of upper arm tissues. After clearing the axillary tissues, the lymphatic tissues located in the axilla are damaged, resulting in poor lymphatic return to the upper arm, stiffness of the tissues in the upper arm, and pain when moving. Surgical damage to the nerves or postoperative infections may also occur. 2. Other factors, mostly referring to the patients who receive postoperative radiotherapy, due to the tissue edema caused by radiotherapy, can also cause the patients to have different degrees of pain in the upper limbs when moving. In addition, nerve compression caused by tumor lymph node metastasis will also occur. If the pain in the affected limbs occurs after breast cancer surgery, consult the doctor in time to clarify the cause of the disease and deal with it actively.