This is an open-label, multicenter, randomized phase 3 trial. Eligible patients are women with cN3 breast cancer who have completed neoadjuvant systemic therapy (NST), undergone breast/axillary surgery with the internal mammary, supraclavicular, and infraclavicular nodes left undissected, and have no macroscopic residual disease in these stations on post-NAT \[¹⁸F\]FDG PET-CT or other imagings. The primary endpoint is 3-year invasive breast cancer recurrence-free interval (IBCRFI). Secondary endpoints include locoregional recurrence-free survival, distant metastasis-free survival, disease-free survival, overall survival, toxicity, and patient reported outcomes. This trial will provide high-level evidence on the safety of nodal boost omission in cN3 breast cancer patients with clinical complete response after NST. If non-inferiority is confirmed, this strategy could establish a new, toxicity-sparing standard for regional nodal irradiation in this high-risk population.