This multicenter, open-label, single-arm, Phase IIIb study will evaluate the safety and tolerability of pertuzumab in combination with trastuzumab (Herceptin) and a taxane (docetaxel, paclitaxel or nab-paclitaxel) in first-line treatment in participants with metastatic or locally recurrent HER2-positive breast cancer. Participants will receive pertuzumab intravenously (IV) and trastuzumab (Herceptin) IV plus a taxane in cycles of 3 weeks each until predefined study end, unacceptable toxicity, withdrawal of consent, disease progression, or death, whichever occurs first.