A Study of an Alternative Treatment Approach (Preoperative Radiotherapy, Then Mastectomy, Then Immediate Reconstruction Surgery) in People With T4 Breast Cancer

Participants will undergo pre-NART core biopsy guided by post-NAC MRI to the area of residual enhancement or to the previously biopsied cancer if no residual enhancement remains

After biopsy, participants will undergo neoadjuvant radiotherapy/NART

At 2-6 weeks after completion of NART, participants will undergo unilateral MRM (total mastectomy with axillary lymph node dissection), with resection of all involved breast skin. Skin-sparing mastectomy will not be permitted. All patients will also undergo simultaneous unilateral autologous-based breast reconstruction with DIEP, ms-TRAM, or latissimus dorsi flap.