A Randomized, 3 Arm, Multicenter, Phase III Study to Evaluate the Efficacy and the Safety of T-DM1 Combined With Pertuzumab or T-DM1 Combined With Pertuzumab-Placebo (Blinded for Pertuzumab), Versus the Combination of Trastuzumab Plus Taxane, as First Line Treatment in HER2 Positive Progressive or Recurrent Locally Advanced or Metastatic Breast Cancer

This randomized, 3-arm, multicenter, phase III study will evaluate the efficacy and safety of trastuzumab emtansine (T-DM1) with pertuzumab or trastuzumab emtansine (T-DM1) with pertuzumab-placebo (blinded for pertuzumab), versus the combination of trastuzumab (Herceptin) plus taxane (docetaxel or paclitaxel) in participants with HER2-positive progressive or recurrent locally advanced or previously untreated metastatic breast cancer. Participants will be randomized to 1 of 3 treatment arms (Arms A, B or C). Arm A will be open-label, whereas Arms B and C will be blinded.