Overall Number of Participants Who Experienced at Least One Adverse Event, Including Serious and Non-Serious Adverse Events, by Most Severe Intensity (According to NCI-CTCAE v3.0) During the Treatment Period

Placebo + Trastuzumab + Docetaxel

This is the placebo safety population, which includes participants who received study treatment with placebo at every cycle. Participants received placebo IV q3w and trastuzumab 6 mg/kg IV q3w, plus docetaxel 75 mg/m\^2 IV q3w (for at least 6 cycles; 1 cycle was 21 days). After Cycle 6, continuation of docetaxel treatment was at the discretion of the participant and treating physician. Participants remained in the treatment phase of the study until investigator-assessed radiographic or clinical evidence of disease progression, unmanageable toxicity, or study termination and were followed for survival until death, loss to follow-up, withdrawal of consent, or study termination.

Pertuzumab + Trastuzumab + Docetaxel

This is the pertuzumab safety population, which includes participants who received at least one dose of study treatment with pertuzumab. Participants received pertuzumab 420 milligrams (mg) intravenously (IV) once every 3 weeks (q3w) and trastuzumab 6 milligrams per kilogram (mg/kg) IV q3w, plus docetaxel 75 milligrams per square metre of body surface (mg/m\^2) IV q3w (for at least 6 cycles; 1 cycle was 21 days). After Cycle 6, continuation of docetaxel treatment was at the discretion of the participant and treating physician. Participants remained in the treatment phase of the study until investigator-assessed radiographic or clinical evidence of disease progression, unmanageable toxicity, or study termination and were followed for survival until death, loss to follow-up, withdrawal of consent, or study termination.

Crossover From Placebo to Pertuzumab

Fifty of 406 participants (12.3%) randomized to the placebo treatment arm whose disease had not progressed crossed over to an open-label pertuzumab treatment group between July 2012 and November 2018. Participants received pertuzumab administered as an IV loading dose of 840 mg at cycle 1 then 420 mg IV every q3w. Trastuzumab and docetaxel doses continued in accordance with the pre-crossover placebo treatment regimens and according to dosing specifications indicated in the study protocol. Participants remained in the treatment phase of the study until investigator-assessed radiographic or clinical evidence of disease progression, unmanageable toxicity, or study termination and were followed for survival until death, loss to follow-up, withdrawal of consent, or study termination.

Analysis denominator · Participants