Study hypothesis is that combining the advantages of hybrid PET/MRI and the high sensitivity/specificity of 16-alpha-18F-fluoro-17-beta-estradiol(FES), a radiolabeled form of estrogen binding to functionally active ER, the investigators could obtain a reliable, non-invasive, operator-independent, one-stage imaging method for staging LumA and ER-positive Lobular tumours.

This is a single-centre prospective cohort study where patients with LumA and ER-positive Lob will be enrolled in 1 cohort undergoing: primary surgery; . Aim : Evaluating the performance of FES PET/MRI in axillary staging compared with axillary surgery. Additionally, biological determinants of tumor heterogeneity will be investigated.

Inclusion Criteria:

• Female patients, age>= 18 yrs, diagnosed with primary or advanced breast cancer

• LumA or ER-positive Lobular subtypes

  • candidates to surgery as first treatment regardless of cN
  • ER-positive Her2 negative BC with ki67>10%

Exclusion Criteria:

• ER-negative tumors
• Pregnancy;
• Contraindication to PET;
• Contraindication to MRI;
• Claustrophobia;
• Allergy to the MR contrast agent;
• Severe renal insufficiency