The principles of postoperative radiotherapy for breast cancer: No postoperative radiotherapy after radical surgery for stage I breast cancer without special indications. Stage II breast cancer patients with negative axillary lymph nodes are not treated with radiotherapy, and it is controversial whether to treat 1-3 axillary lymph node metastases with radiotherapy. However, some studies have shown that radiotherapy can also increase the effectiveness of local control and systemic control. Radiotherapy is required for 4 or more axillary lymph node metastases. All stage III breast cancers require radiation therapy, but the field of radiation therapy is different. If the lymph nodes are negative, only the chest wall is irradiated; if there are 1-3 metastases in the axillary lymph nodes, the supraclavicular and chest wall are irradiated; if there are more than 4 metastases or metastases in the subclavicular lymph nodes, the chest wall, internal breast area and supraclavicular are irradiated. However, for those who have residual lesions in the axilla that are difficult to be removed by surgery and exceed 2 cm, or those who have cancer clots in the axillary vessels, additional axillary irradiation can be added. Indications and principles of postoperative radiotherapy for breast cancer 1. Indications for postoperative radiotherapy for breast cancer: (1) tumor located in the central belt or inside the breast; (2) axillary node (+); (3) tumor diameter >5.0 cm; (4) tumor fixed with pectoral fascia; (5) invasion of skin; (6) multiple lesions; (7) involvement of blood vessels, nerves and lymph nodes. 2.Specific principles: (1) clinical stage I-II axillary nodes (-) can not be radiotherapy; (2) axillary nodes (+) 1 to 3, can consider the supraclavicular area and internal breast area radiotherapy; (3) axillary nodes (+) ≥ 4 should be radiotherapy in the upper and lower clavicular area and internal breast area, and additional radiation chest wall. (3) Special cases: (1) Axillary node clearance is relatively smooth, and radiotherapy is generally not needed for the axilla, because some unnecessary radiotherapy may cause or aggravate the edema of the affected upper limb and affect the patient’s quality of survival. (2) If axillary node excision is difficult and residual is estimated, radiotherapy should be done. (3) Breast cancer is a systemic disease, radiotherapy as local treatment cannot resolve distant metastasis. (4) For invasive cancer, chemotherapy should be applied first after surgery. High-risk patients with more axillary lymph nodes (+) can be considered for hematopoietic stem cell transplantation and high-dose chemotherapy. (5) Postoperative radiotherapy, as part of the comprehensive treatment of breast cancer, should be applied in coordination with adjuvant chemotherapy and/or endocrine therapy according to the patient’s specific situation. The most controversial indication for post-mastectomy radiotherapy is still the group of patients with moderate risk of recurrence, i.e., T1-2, with one to three axillary lymph node metastases. Overall, the 10-year chest wall and regional lymph node recurrence rate in this group of patients without adjuvant radiotherapy is about 15%. Some important large samples have been reported in the literature both at home and abroad in the past few years, suggesting that patients meeting the above conditions are in fact a very heterogeneous group, with age under 40 years, tumors under 3 cm, hormone receptor negativity and vascular invasion as high-risk factors, and a 5-year local regional recurrence rate of more than 30% if patients meet 3 or more factors at the same time; in addition the value ratio of lymph node metastases has in recent years The value ratio of lymph node metastasis has been gaining more and more attention in recent years. The 10-year local recurrence rates were 23% and 48% for patients under 45 years of age with ≤25% and >25% lymph node metastases, respectively, and 11% and 27% for those over 45 years of age, respectively. In China, the 5-year chest wall recurrence rate was 12.2% in patients with >30% T2 lymph node metastasis, and Truong et al. also suggested that the recurrence rate was higher in the medial quadrant than in the lateral and central regions for the same proportion of axillary lymph node metastasis and age. In conclusion, the available data prefer to distinguish between relatively high-risk and low-risk groups for patients with the traditional concept of “intermediate risk” of recurrence, which is the main target of current clinical studies.