Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab emtansine plus pertuzumab. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the pertuzumab IV infusion, on Day 1 of each 3-week cycle. Pertuzumab was given as 840 mg IV on Day 1 of Cycle 1, then 420 mg IV on Day 1 of each subsequent 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.

Participants received trastuzumab plus either docetaxel or paclitaxel. The regimen was chosen at the investigator's discretion. Option 1: trastuzumab 8 mg/kg via IV infusion on Day 1 of Cycle 1, then 6 mg/kg IV on Day 1 of each subsequent 3-week cycle; plus a minimum of 6 cycles with docetaxel 75 or 100 mg/m^2 IV on Day 1 of each 3-week cycle. Option 2: trastuzumab 4 mg/kg IV on Day 1 of Cycle 1, then 2 mg/kg IV weekly beginning on Day 8 of Cycle 1; plus a minimum of 18 weeks with paclitaxel 80 mg/m^2 IV weekly. Treatment continued until disease progression, unacceptable toxicity, or study termination. If trastuzumab or docetaxel were discontinued for toxicity, the other agent could be continued as monotherapy.

Participants received trastuzumab emtansine plus pertuzumab-placebo. Trastuzumab emtansine was administered as 3.6 mg/kg via IV infusion, following completion of the placebo IV infusion, on Day 1 of each 3-week cycle. Treatment continued until disease progression, unacceptable toxicity, or study termination.