Research purpose: Lymphedema is a very common complication in breast cancer patients. However, since there is currently no curable treatment, it is important to prevent and reduce the severity of lymphedema. The purpose of this study is to evaluate whether preoperative exercise is effective in preventing lymphedema after surgery. For secondary outcome, the preventive effects of exercise on other upper extremity dysfunctions (eg. pectoralis tightness, Axillary web syndrome, Adhesive capsulitis), which are common in breast cancer patients, were assessed.