This single arm study aims to evaluate the efficacy and safety of a non-surgical approach, consisting of radiotherapy (RT) alone, for patients who have achieved a complete pathological response (pCR) following neoadjuvant chemotherapy (NACT). The study design involves the histological confirmation of pCR using vacuum-assisted biopsy (VABB) or vacuum-assisted excision (VAE) guided by ultrasound. The primary objective is to demonstrate that the non-surgical, RT-only treatment and follow-up approach is not inferior to the traditional surgical approach in patients with pCR after NACT.