Patients treated with ado-trastuzumab emtansine (T-DM1) in this study had more advanced breast cancer than patients treated in the clinical trials and received T-DM1 in later lines of therapy.

Patients treated with T-DM1 in this study had shorter treatment periods and survival than in the clinical trials, which suggests the need for additional therapies.

In our study, over half of the patients received pertuzumab prior to T-DM1, and their treatment patterns and outcomes appeared similar for patients who did not receive prior pertuzumab.

These real-world data shed light on treatment patterns and outcomes in patients with HER2-positive metastatic breast cancer who receive treatment post–T-DM1.