⁃ Patients eligible for inclusion in this study must meet all the following criteria:

• Female patients with invasive, untreated HER2+ breast cancer (as assessed by local pathology) maximum 6 weeks before registration (standard-of-care diagnostic biopsy according to current AGO guidelines)

• Age ≥18 years 3a. Cohort 1: low- to intermediate-risk for recurrence as per investigator´s decision (recommendation: cT1c - cT2 (1 - ≤3cm), cN0; cT1a/b excluded), OR 3b. Cohort 2: intermediate- to high-risk for recurrence as per investigator´s decision (recommendation: cT2 (\>3 - ≤5cm), cN0) 3c. Elderly patients (≥ 65 years) may be assigned to any cohort as per investigator's decision

⁃ 4\. Written informed consent 5. LVEF ≥ 50% within 28 days before randomisation 6. Eastern Cooperative Oncology Group performance status (ECOG PS) 0-1 7. Adequate organ and bone marrow function within 14 days before randomisation 8. Adequate treatment washout period before randomisation (refer to protocol for detailed information) 9. Evidence of post-menopausal status or negative serum pregnancy test for females of childbearing potential (refer to protocol for detailed information) 10. Female subjects must not donate, or retrieve for their own use, ova from the time of randomisation and throughout the study treatment period, and for at least 7 months after the final study drug administration. (refer to protocol for detailed information)