HYPOTHESIS: Hybrid PET/MRI might be a non-invasive, one-stage, operator-independent imaging modality to accurately define nodal status after PST, properly select type of surgical approach and might eventually lead to the omission of axillar surgery in some breast cancer patients showing complete imaging response.
AIMS: The primary endpoint is to compare the staging power between SNB (or lymphoadenectomy) vs PET/MRI in detecting axillary lymph node macro-metastases (\>2 mm).Additionally the PET/MRI and A-US results will be confronted and ultimately related to pathology result, calculating the concordance rate in terms of positive vs negative nodes and number of positive nodes detected by each method. The staging power of both preoperative exams will be evaluated by considering how many times the results from PET/MRI or A-US could have indicated the most appropriate axillary treatment according to pathological findings.
EXPERIMENTAL DESIGN: Patients with breast cancer of any size with positive axillary nodes and candidates to PST will undergo PET/MRI prior to PST.
The study population will then be split into two groups:
* women with positive axillary lymph nodes after PST (Group 1, 60% of the total)
* women with negative axillary lymph nodes after PST (Group 2, 40% of the total).
A total of 110 women will guarantee two well-powered independent analysis. one for Group 1 (n=66; power\>90%; Type I error rate of 0.05) and one for Group 2 (n=44; power\>80%; Type I error rate of 0.05).
