 This was a multi-institutional, multinational, open-label, single-arm Phase IbII study designed to evaluate the safety, tolerability, pharmacokinetics, and efficacy of trastuzumab emtansine trastuzumab-MCC-DM1 administered by intravenous IV infusion in combination with pertuzumab in patients with human epidermal growth factor receptor-2 HER2-positive locally advanced or metastatic breast cancer who had previously received trastuzumab. 