An Exploratory Phase II, Single-Arm, Multicenter Study to Evaluate the Efficacy and Safety of the Combination of Pertuzumab and Herceptin (Trastuzumab) in Patients With HER2-Positive Metastatic Breast Cancer

This study will evaluate the efficacy and safety of Perjeta (pertuzumab) in combination with Herceptin (trastuzumab) in participants with metastatic breast cancer who have progressed on trastuzumab-based therapy (Cohorts 1 and 2), and will make a preliminary assessment of the efficacy and safety of single-agent pertuzumab (Cohort 3). Objective response rate and clinical benefit will be assessed. Pertuzumab will be administered at an initial dose of 840 milligrams (mg) intravenously (IV) on Day 1, followed by 420 mg IV every 3 weeks. Trastuzumab will be administered at the same schedule the participant was following before entry into the study. An additional cohort of participants at certain centers will receive pertuzumab monotherapy at an initial dose of 840 mg IV on Day 1, followed by 420 mg IV every 3 weeks. These participants may have trastuzumab added to the regimen in the event of progression during single-agent pertuzumab treatment.