The Postoperative Radiotherapy in N1 Breast Cancer Patients

Inclusion Criteria: * Patients aged 19 years or older. * A female patient who underwent breast-conserving surgery or mastectomy for invasive breast cancer. * Patient with stage pN1 after surgery on histopathologic examination. * However, if mastectomy was performed, 5 or more nodes should be resected in the case of 1 positive node, and axillary lymph node dissection (ALND) should be performed in case of 2 or 3 positive nodes. * Patients undergoing or planning to undergo hormone therapy in the case of hormone receptor positive. * Patients who have received or are expected to undergo targeted therapy in the case of human epidermal growth factor receptor(HER)-2 positive. * Patients with Eastern Cooperative Oncology Group (ECOG) Scale 0-2. * Patients who agreed to participate in the study. Exclusion Criteria: * Patients who have received prior \[neoadjuvant\] chemotherapy. * Patients receiving radiation therapy for salvage or palliative purposes. * Patients with stage T4. * Patients with ipsilateral supraclavicular and internal mammary lymph node metastases or distant metastases. * Male breast cancer patient. * Patients who have previously received radiation therapy to the ipsilateral breast or supraclavicular region. * Patients having a history of cancer other than thyroid cancer, cervical carcinoma in situ, or skin cancer. * Patients diagnosed with ductal breast carcinoma in situ, lobular carcinoma in situ, phyllodes, metaplastic cancer, or benign tumors based on histological diagnosis.