To prospectively evaluate the impact of HER2DX on the decision-making processes of the treating physicians and especially among the routine multidisciplinary tumour board, in defining type and setting of systemic therapy administration in patients with stage I-III HER2+ BC, and the degree of clinician's confidence in the treatment recommendation.

Inclusion Criteria:

• Patients ≥ 18 years of age;
• Histologically confirmed HER2+ breast cancer;
• Stage I-III breast cancer without evidence of distant metastases;
• Being candidate to neoadjuvant/adjuvant therapy and locoregional treatment (surgery +/- radiotherapy);
• Written informed consent, signed by the patient, to study-specific procedures (the consent will consist of 2 levels: level 1 specifically for patients enrolled in the primary endpoint cohort and level 2 for all patients);

Exclusion Criteria:

• HER2- BC;
• Stage IV breast cancer;
• Lack of informed consent because of patient's incapable of discernment or unwilling to participate;

HER2 positive breast cancer patients with stage I-III