Boost Irradiation to the Supraclavicular Area Among High Risk cN3c Breast Cancer Patients

Inclusion Criteria: * Voluntary participation with documented informed consent. * Females aged ≥18 years. * Histological or cytological confirmed primary breast carcinoma. * Clinical diagnosis of cN3c. * Receipt of neoadjuvant therapy, guided by the attending physician and current treatment guidelines. * Did not achieve cCR in SCLN following neoadjuvant therapy. * Undergoing curative-intent breast cancer surgery post-neoadjuvant therapy. * Pathological evaluation of axillary lymph nodes post-surgery. * KPS score ≥80, with expected survival exceeding 2 years. * Complete healing of surgical incision without complications. * Negative pathological surgical margins. * Availability of hormonal receptor (ER/PR), HER2, and Ki-67 status for the primary breast lesion. * Pre-menopausal females required to practice contraception for at least one month prior to screening, maintaining contraception throughout the study and for a specified period post-study cessation. Exclusion Criteria: * Patients with confirmed distant metastases by pathology or imaging. * Those who have not received neoadjuvant systemic therapy. * Patients who have not undergone curative-intent surgery. * Pregnant or lactating women. * Individuals with severe non-neoplastic comorbidities affecting radiotherapy implementation. * History of malignancy within the past 5 years (excluding ductal carcinoma in situ, basal cell carcinoma, squamous cell carcinoma in situ, cervical carcinoma in situ, and in situ adenocarcinoma of the lung). * Simultaneous contralateral breast cancer. * History of prior radiation therapy to the neck, chest, or ipsilateral axilla. * Active collagen vascular disease. * Patients with T4 staging of the primary tumor. * Inability to initiate radiotherapy within 12 weeks post breast cancer curative surgery (breast-conserving surgery or mastectomy), or within 8 weeks post completion of adjuvant chemotherapy.