The gold standard of surgical treatment for patients with early breast cancer (BC) is breast conservation and sentinel node biopsy (SNB). Ongoing randomized trials are evaluating to omit surgery at all when axillary imaging is negative. However, the available diagnostic tools still have several limitations in accuracy.

Combining the specificity of PET, with the superior sensitivity of MRI, hybrid PET/MRI might be a non-invasive, one-stage, operator-independent imaging method to accurately define nodal status and, whenever negative, might replace surgery for axillary staging.

The project includes patients with <3 cm BC without overt nodal involvement who will undergo PET/MRI prior to surgery. The primary aim is to compare the staging power between SNB and PET/MRI in detecting axillary lymph node macrometastases (>2 mm). Additionally, general concordance and diagnostic accuracy of PET/MRI vs SNB, eventual correlation with BC molecular subtypes and MRI findings will be evaluated.

SNB is the gold standard for axillary staging in early BC patients. Although being a minimally invasive, it is time consuming both for surgeon and pathologist, it may add a further scar and is not free from complications: seroma, limitation of shoulder movement, nerve injury, lymphedema. To date, patients undergoing breast conserving surgery (BCS) with 1 to 2 positive nodes can be treated with SNB alone (ACOSOG Z011 trial NCT00003855[2-4]) and researchers are evaluating within large randomized trials to even omit surgery at all when axillary imaging is negative (SOUND (Sentinel node biopsy vs Observation after axillary Ultra-souND), PI and Study Chair Dr.O.Gentilini,MD, NCT02167490 and INSEMA (Intergroup-SEntinel-MAmma) trial NCT02466737.

While the role of surgery is decreasing, the role of preoperative imaging is increasing. In the future, imaging might even replace surgery in the axillary staging of BC patients, still providing an appropriate level of information to guide medical treatments which are more and more tailored on biology rather than on nodal status. In this context, an unmet need is to achieve the most accurate preoperative imaging assessment of the axilla in order to decide the appropriate treatment for each patient.

The hypothesis of this project is that PET/MRI might provide a single, one-stage, non-invasive, operator independent imaging modality in patients with small BC allowing to select the proper treatment for patients. PET/MRI is a relatively new imaging tool and its field of application is still object of scientific speculation.

Inclusion Criteria:

• signed Informed Consent
• age > 18
• non palpable lymph nodes
• no suspicious nodes at A-US (Axillary- ultrasound)
• candidate to mastectomy or breast conserving surgery and BLS (Sentinel Node Biopsy)

Exclusion Criteria:

• pregnancy
• distant metastasis
• inflammatory cancer
• claustrophobia
• allergy to contrast agent
• severe renal insufficiency