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.

Neoadjuvant chemotherapy (NACT) in breast cancer is considered the "gold standard" for the treatment of locally advanced and inoperable malignancies.

In recent years, in view of the evidence gathered, it has also become a conventional treatment alternative for patients with operable disease who are possible candidates for adjuvant chemotherapy. NACT thus aims to reduce mortality and increase surgical options, while at the same time allowing in vivo chemosensitivity testing. In view of this, NACT represents the ideal setting for clinical and translational research, which nowadays also has to address the question of future treatment options.

It is indeed a source of lively debate whether chemotherapy should be considered the only possible treatment option for the patient.

This study falls into this context, the innovative aim of which is to demonstrate histologically with the use of VABB, the complete pathological response (pCR) and to avoid surgery.

The main aim of this study is to show that a non-surgical, radiotherapy-only treatment and follow-up approach is not inferior to a surgical approach for patients who have shown complete pathological response (pCR) following neoadjuvant chemotherapy (NACT), as confirmed through histological analysis of imaging-guided sampling.

Histology will be performed by sampling 4 grams of tissue by vacuum-assisted biopsy (VABB) or vacuum-assisted excision (VAE) by ultrasound guidance (on breast marker).

The hypothesis of the study is that the VAE/VABB will be used in patients with pCR at post-NACT imaging to demonstrate the absence of disease in the previous tumour bed and, accordingly, that the use of VAE/VABB with negative histology would lead to a gold standard of treatment without surgical overtreatment.

Inclusion Criteria:

• age> 18 years
• infiltrating breast carcinoma, non-special histotype, triple negative or HER2 +, T1-T2 N0
• single lesion
• neo-adjuvant chemotherapy treatment for at least 12 weeks according to clinical practice
• conservative surgery proposal
• M0
• tumour bed identified by breast markers placed in pre NACT by radiologist

Exclusion Criteria:

• Bilateral or multicentric tumour
• Presence of microcalcifications visualised on mammography
• Presence of associated DCIS
• Positive history of previous breast cancer
• Positive history of medical or psychiatric conditions preventing adherence to the protocol
• High risk patient