Radiotherapy and Long-term Outcomes in Early Breast Cancer With SLNB Omission

Inclusion Criteria: * Female patients aged 19 years or older with histologically confirmed invasive breast cancer * Patients who have undergone breast-conserving surgery with curative intent * Patients who did not undergo axillary lymph node surgery, including sentinel lymph node biopsy, at the time of breast cancer surgery * No evidence of distant metastasis on clinical and imaging evaluation before surgery * Planned to receive adjuvant radiotherapy after breast-conserving surgery * Ability and willingness to provide written informed consent before study participation Exclusion Criteria: * Patients initially diagnosed with breast carcinoma in situ before surgery who did not undergo sentinel lymph node biopsy but were subsequently found to have invasive breast cancer on final surgical pathology * Receipt of neoadjuvant systemic therapy before breast cancer surgery * History of a malignancy other than breast cancer within 5 years before study enrollment, except adequately treated non-melanoma skin cancer or carcinoma in situ other than breast carcinoma in situ * Recurrent breast cancer * Bilateral breast cancer or inflammatory breast cancer * Prior radiotherapy to the ipsilateral breast or chest region * Patients considered by the investigator to be unsuitable for study participation or long-term follow-up