In HER2-positive metastatic breast cancer, trastuzumab based treatment is the standard of
care as long as there are no contraindications to trastuzumab. Frequently, trastuzumab is
being combined with taxanes in the first-line setting. However, since therapy with
trastuzumab is active even in the absence of chemotherapy in HER2-positive MBC, the optimal
treatment strategy either in combination or in sequence with chemotherapy is still under
debate. This randomized phase II trial is studying a new strategy for the treatment of
metastatic breast cancer with HER2-positive. First-line treatment consists of trastuzumab and
pertuzumab, a treatment without chemotherapy. In case of disease progression, chemotherapy
with T-DM1 is then performed as second-line treatment. Third-line and further line therapies
are performed according to the physician's discretion. If this new therapeutic strategy is as
effective and better tolerated than the conventional strategy, this would mean a serious
breakthrough in the treatment of HER2-positive metastatic breast cancer.