A Study of Pertuzumab in Combination With Trastuzumab Plus an Aromatase Inhibitor in Participants With Metastatic Human Epidermal Growth Factor Receptor 2 (HER2)-Positive and Hormone Receptor-Positive Advanced Breast Cancer

This randomized, open-label, two-arm, multi-center, Phase II study will evaluate the efficacy and safety of pertuzumab in combination with trastuzumab plus an aromatase inhibitor (AI) in first-line participants with HER2-positive and hormone receptor-positive advanced breast cancer. Participants will be randomized to one of two treatment arms; Arm A (pertuzumab in combination with trastuzumab plus an AI) or Arm B (trastuzumab plus an AI). Participants may also receive induction chemotherapy (a taxane, either docetaxel or paclitaxel) at the investigator\'s discretion in combination with the assigned treatment arm. The anticipated time on study treatment is until disease progression, unacceptable toxicity, withdrawal of consent, or death whichever occurs first.