Level I-II Axillary Irradiation in Breast Cancer With Sentinel-Node Macro-metastases

Inclusion Criteria: 1. Female ≥ 18 years of age; 2. Newly diagnosed primary invasive breast cancer; 3. Clinically stage T1-3N0M0; 4. Patients received surgery as first treatment,and have undergone breast conserving-surgery or mastectomy (with or without breast reconstruction) with negative margins; 5. Have one or two macrometastases (\>2 mm) at sentinel lymph node biopsy,and without further axillary lymph node dissection; 6. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1; 7. Will receive endocrine therapy for at least 5 years for estrogen receptor (ER) and/or progesterone receptor (PR) positive patients; will receive anti-HER2 (human epidermal growth factor receptor 2) therapy for 1 year for HER2 positive patients; 8. Radiation therapy must begin no later than 12 weeks after the last dose of adjuvant chemotherapy or the last breast cancer surgery if no adjuvant chemotherapy; 9. Patients have adequate organ function; 10. Acquirement of informed consent. Exclusion Criteria: 1. Patients have received neoadjuvant systemic therapy; 2. Clinical stage T4 or IV (metastatic) breast cancer, or presence of regional metastases before surgery; 3. History of any prior ipsilateral or contralateral invasive breast cancer, history of other malignancies except for appropriately treated skin basal cell carcinoma and cervical carcinoma in situ; 4. History of previous radiotherapy towards the ipsilateral chest/lymph nodes. 5. The ipsilateral axillary lymph node dissection or other previous axillary surgery; 6. Current severe, uncontrolled systemic disease (e.g., clinically significant cardiovascular, pulmonary, hepatic, renal, hematologic, or psychiatric disease), inability to tolerate radiotherapy or systemic therapy if indicated; 7. Current pregnancy and/or lactation; 8. Inability or unwillingness to comply with protocol requirements.