• Signed written informed consent

• Histologically confirmed primary invasive breast cancer

• Stage II - IIIA primary breast cancer according to TNM-staging (8th edition, AJCC); (largest tumor diameter on DCE-MRI ≥ 2cm (cT2-3) and/or cN1-2 confirmed with FNA or histology)

• HER2 overexpression defined as circumferential membrane staining that is complete, intense and in \>10% of invasive tumor cells (IHC 3+) on pre-treatment biopsy

• Known estrogen- and progesterone-receptor expression of the invasive tumor

• a. ER-negative or PR-negative is defined as \<10% of invasive tumor cell nuclei are immunoreactive in the presence of evidence that the sample can express ER and/or PR

• WHO performance status 0-1

• Age ≥ 18 years

• LVEF ≥50% measured by echocardiography or MUGA

• Eligible for neoadjuvant treatment

⁃ Laboratory requirements within 21 days prior to enrollment:

∙ Adequate bone marrow function (ANC ≥1.5 x 109/l, platelets ≥100 x 109/l);

‣ Adequate hepatic function (ALAT, ASAT and bilirubin ≤2.5 times upper limit of normal). Subjects with Gilbert's syndrome may have a total bilirubin ≥2.5 × the ULN range, if no evidence of biliary obstruction exists.

‣ Adequate renal function: creatinine clearance \>50 ml/min estimated using the Cockcroft-Gault equation or MDRD equation, or based on a 24-hour urine collection measurement.