Radiotherapy Dose Adaptation Based on Tumor Biology in Patients With cN2b-N3 Breast Cancer

The purpose of the study is to evaluate treatment outcomes of breast cancer with internal mammary or supraclavicular lymph node metastasis according to total radiation dose of postoperative radiation therapy differentiated by tumor response to neoadjuvant chemotherapy. The main questions it aims to answer are: * 5-year disease-free survival * 5-year overall survival * 5-year locoregional recurrence * Adverse events after radiation therapy * Quality of life Participants will be assessed by multi-dimensional methods before and after radiotherapy: * Disease status evaluation including physical and radiological examination * Quality of life assessment with questionnaires (BREAST-Q) * Adverse event assessment according to CTCAE version 5.0