Italian multicentric non inferiority clinical study to verify whether the omission of axillary lymph node intervention in patients with SLN (Sentinel Lymph Nodes) ypN1mi after NAC (Neo Adiuvant Chemotherapy) does not lead to a significant deterioration in survival or in the risk of regional or distant recurrence, compared to patients with negative SLN (SLN ypN0) after NAC ,where the omission of axillary treatment is currently the standard treatment.

The study includes patients with cN+ positive axillary lymph nodes at initial diagnosis and who also have negative clinical and instrumental evaluation after NAC. Based on the sentinel lymph nodes definitive histological evaluation patients are allocated in one of the 2 comparison groups (Group 1 experimental or Group 2 standard) or in Group 3 internal control group. Group 3 is not used in statistical comparison with the other two groups but it's aim is to evaluate the appropriateness of the cases.

Referring to bio-pathologic characteristics after surgery patients will receive:

• no further treatment
• complementary radiotherapy
• adjuvant medical therapy (hormonal therapy and/or biological therapy)

Irradiation:

Group 1 (experimental) and Group 2 (standard): irradiation won't be performed neither in the axillary region nor in the other lymph node stations

Group 3 (internal control): after conservative or radical surgery, patients will be subjected to loco-regional irradiation according to Guidelines.

Duration:

Patients enrollment in the study protocol will last for 3 years. Patients will have to be followed for the subsequent 5 years during which they will have to undergo to periodic visits and follow-up checks provided for by the current standard guidelines:

• clinical examination every six months for the first 5 years
• mammography and breast ultrasound yearly
• axillary ultrasound yearly

Inclusion Criteria:

1. Age: 18 ≤75 years
2. Breast carcinoma with infiltrating histotype
3. Tumor size: cT1 - cT2 - cT3
4. Positive axillary lymph nodes (cN +) at the initial diagnosis by clinical, ultrasound and cyto-microhistology evaluation
5. Neoadjuvant chemotherapy performed
6. Negative axillary lymph nodes (cN-) from the NAC by clinical and ultrasound assessment
7. Absence of distant metastases (M0)
8. Negative medical history for previous infiltrating breast cancer

Exclusion Criteria:

1. Current pregnancy or lactation status
2. Inflammatory breast cancer
3. In situ breast cancer
4. Synchronous contralateral breast cancer
5. Co-morbidity and/or medical disorder precluding any adjuvant therapy
6. Co-morbidity and/or medical/mental disorder making impossible making a regular follow-up
7. Other cancers in the previous 3 years (except forcarcinoma in situ of the uterine cervix, basalioma, squamous cell carcinoma or non-melanoma skin cancer)