Critères d'inclusion : - Female patients with histologically-confirmed, unresectable locally advanced or metastatic breast cancer;
- Patients should have had either progression during or after at least two HER2-targeting treatment regimens for locally advanced or metastatic disease or progression during or after (ado-)trastuzumab emtansine treatment for locally advanced or metastatic disease;
- HER2-positive tumor status;
- Patients must have measurable or non-measurable disease that is evaluable per RECIST 1.1;
- Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2;
- Estimated life expectancy > 12 weeks at randomization;
- Adequate organ function and blood cell counts.
Critères de non-inclusion : - Current or previous use of a prohibited medication as listed in the protocol;
- History of infusion-related reactions and/or hypersensitivity to trastuzumab, (ado-)trastuzumab emtansine;
- History of keratitis;
- Severe, uncontrolled systemic disease at screening;
- Left Ventricular Ejection Fraction (LVEF) < 50%, or a history of clinically significant decrease in LVEF during previous treatment with trastuzumab or (ado-)trastuzumab emtansine;
- Cardiac troponin value above the Upper Limit of Normal (ULN);
- History of clinically significant cardiovascular disease;
- Untreated brain metastases, symptomatic brain metastases, brain metastases requiring steroids to manage symptoms, or treatment for brain metastases within 8 weeks prior to randomization;
- History of idiopathic pulmonary fibrosis, organizing pneumonia (e.g., bronchiolitis obliterans), drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest CT scan.