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Editor’s note: Trastuzumab has clearly revolutionized the treatment of HER2-positive breast cancer, both in the metastatic setting and in the adjuvant setting. Nevertheless, de novo and acquired resistance to trastuzumab is evident, with several strategies currently being investigated to overcome resistance. The current study, which in online form preceded its oral presentation at the San Antonio Breast Cancer Symposium by 48 h (San Antonio, TX, USA, December 6–10, 2011), tested the addition of pertuzumab to trastuzumab and docetaxel in patients with HER2-positive metastatic breast cancer.