Response-Based Local Therapy for Regionally Advanced Breast Cancer

Prior treatment

• Presence of severe or uncontrolled concomitant diseases, including severe cardiac dysfunction; myocardial infarction, uncontrolled arrhythmia, or unstable angina within 3 months prior to enrollment; clinically significant pericardial disease; or severe pulmonary disease.
• Prior radiotherapy to the chest wall or supraclavicular region.
• History of or concurrent second primary malignancy, except for non-melanoma skin cancer, papillary or follicular thyroid carcinoma, carcinoma in situ of the cervix, contralateral non-invasive breast cancer, or other malignancies treated with curative intent with no evidence of disease for more than 3 years.

Other illness

• Evidence of distant metastatic disease.
• Pregnancy, lactation, or any condition considered by the investigator to contraindicate radiotherapy.

• Female patients aged 18 to 75 years.
• ECOG performance status ≤ 2.
• Histologically confirmed invasive breast cancer.
• Newly diagnosed breast cancer with pathologically confirmed positive ipsilateral supraclavicular lymph nodes (ISLN) and/or internal mammary lymph nodes (IMLN); for patients in whom IMLN biopsy is not feasible, clinically positive IMLN based on investigator assessment and imaging findings is acceptable.
• Planned to receive neoadjuvant systemic therapy followed by breast-conserving surgery or mastectomy and axillary lymph node dissection, with or without supraclavicular and/or internal mammary lymph node dissection.
• Adequate baseline organ function, defined as: absolute neutrophil count ≥ 1.5 × 10⁹/L; platelet count ≥ 100 × 10⁹/L; hemoglobin ≥ 9 g/dL (90 g/L); serum creatinine ≤ 1.5 × upper limit of normal (ULN) or creatinine clearance ≥ 60 mL/min; total bilirubin ≤ 1.5 × ULN; AST and/or ALT ≤ 2.5 × ULN; INR ≤ 1.5 and PT/APTT ≤ 1.5 × ULN.
• Able and willing to comply with study procedures and scheduled follow-up.
• Written informed consent obtained prior to any study-related procedures.