Participants will receive a loading dose of 8 milligrams per kilogram (mg/kg) as an intravenous infusion on Day 1 or 2 of first treatment cycle, followed by 6 mg/kg on Day 1 or Day 2 of each subsequent treatment 3-week cycles until disease progression or unacceptable toxicity.

Participants will receive 1 mg anastrozole or 2.5 mg letrozole orally once daily.

Participants receiving induction chemotherapy up to the first 18-24 weeks of the treatment period will receive a taxane (docetaxel every 3 weeks or paclitaxel weekly), administered in line with the respective pertuzumab and/or trastuzumab infusions at the investigator's discretion.

The overall response rate (ORR) was defined as the percentage of participants with best (confirmed) overall response (BOR) of either complete response (CR) or partial response (PR) from start of study treatment until progressive disease (PD)/recurrence or death, as assessed by the investigator according to RECIST version 1.1. CR: disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to <10 mm; PR: at least a 30% decrease in the sum of diameters of target lesions, taking as reference baseline sum diameters; stable disease (SD): neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study. Participants needed to have two consecutive assessments of PR or CR at least 4 weeks apart to be a responder. Analysis of this outcome measure was only planned to occur at the time of primary analysis.

Clinical Benefit Rate (CBR) was defined as the percentage of participants with best (confirmed) partial response (PR) or complete response (CR) or stable disease (SD) for at least 6 months. According to RECIST version 1.1, CR: disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to <10 mm; PR: at least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters; SD: neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study. Analysis of this outcome measure was only planned to occur at the time of primary analysis.

Duration of response (DOR) was defined as the period from the date of initial confirmed partial response (PR) or complete response (CR) until the date of progressive disease or death from any cause. According to RECIST version 1.1, CR: disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to <10 mm; PR: at least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. Participants with no documented progression after CR or PR were censored at the last date at which they were known to have had the CR or PR, respectively. The primary analysis of DOR was planned to be performed at the same time as for PFS (when a total of 165 PFS events had occurred), and the final analysis was planned after at least 60 months follow-up for all participants.

Time to Response (TTR) was defined as the time from the date of randomization to the date of first complete response (CR) or partial response (PR). According to RECIST version 1.1, CR: disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to <10 mm; PR: at least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. For participants who did not have a confirmed response, a censored TTR was calculated at the date of the last adequate tumor assessment. If no tumor assessment is performed for the participant (or all post-baseline assessments are not evaluable or PD) the censoring day would be set to day 1 (date of randomization). Analysis of this outcome measure was only planned to occur at the time of primary analysis.

The EQ-5D VAS is a participant-rated questionnaire to assess health-related quality of life (QoL) in terms of a single index value. The VAS component rates current health state on a scale from 0 mm (worst imaginable health state) to 100 mm (best imaginable health state); higher scores indicate a better health state.

All adverse events (AEs) occurring during the study and until the post-treatment safety follow-up visit approximately 28 days after last study medication were recorded; thereafter, only study drug-related serious adverse events (SAEs) continued to be collected. The investigator graded all AEs for severity per the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE), Version 4.03; if not listed, the AE was assessed as follows: Grade 1 = mild; Grade 2 = moderate; Grade 3 = severe; Grade 4 = life-threatening/disabling; Grade 5 = death. The investigator determined whether an AE was related to study drug and independently assessed severity and seriousness of each AE. AEs suggestive of congestive heart failure (CHF) were identified by the SMQ (wide) "Cardiac Failure" with a status of "serious", which included the preferred terms cardiac failure, left ventricular dysfunction, and pulmonary oedema.

The causes of death over the course of the study, regardless of whether the death was related to study treatment, are listed by preferred term according to the Medical Dictionary for Regulatory Activities (MedDRA), version 22.1.

Left ventricular ejection fraction (LVEF) is the measurement of how much blood is being pumped out of the left ventricle of the heart (the main pumping chamber) with each contraction. A normal LVEF ranges from 55% to 70%, as measured by echocardiogram or multiple-gated acquisition (MUGA) scan. All participants must have had a baseline LVEF of at least (≥)50% to enroll in the study; patients with clinically significant cardiovascular disease or baseline LVEF below 50% were not eligible for this study.

Participants received trastuzumab at a loading dose of 8 mg/kg of body weight followed by 6 mg/kg of body weight on Day 1 or Day 2 of each 3-weekly cycle until disease progression, unacceptable toxicity, withdrawal of consent, or death, or the predefined end of study whichever occurred first. Participants also received an aromatase inhibitor (AI), orally as per product labeling (anastrozole: 1 mg once daily or letrozole: 2.5 mg once daily). Participants receiving induction chemotherapy up to the first 18-24 weeks of the treatment period were to receive a taxane (docetaxel every 3 weeks or paclitaxel weekly), administered in line with the respective product labeling.

Safety Population

Final Analysis

Stratified log-rank test based upon Kaplan-Meier including induction chemotherapy and prior adjuvant hormone therapy stratification factors.

Hazard ratio comparing Arm A vs. B from stratified Cox proportional hazards model including stratification factors.

Exploratory

Participants received trastuzumab at a loading dose of 8 mg/kg of body weight followed by 6 mg/kg of body weight on Day 1 or Day 2 of each 3-weekly cycle until disease progression, unacceptable toxicity, withdrawal of consent, or death, or the predefined end of study whichever occurred first. Participants also received an aromatase inhibitor (AI), orally as per product labeling (anastrozole: 1 mg once daily or letrozole: 2.5 mg once daily). Participants receiving induction chemotherapy up to the first 18-24 weeks of the treatment period were to receive a taxane (docetaxel every 3 weeks or paclitaxel weekly), administered in line with the respective product labeling.

Participants received trastuzumab at a loading dose of 8 mg/kg of body weight followed by 6 mg/kg of body weight on Day 1 or Day 2 of each 3-weekly cycle until disease progression, unacceptable toxicity, withdrawal of consent, or death, or the predefined end of study whichever occurred first. Participants also received an aromatase inhibitor (AI), orally as per product labeling (anastrozole: 1 mg once daily or letrozole: 2.5 mg once daily). Participants receiving induction chemotherapy up to the first 18-24 weeks of the treatment period were to receive a taxane (docetaxel every 3 weeks or paclitaxel weekly), administered in line with the respective product labeling.

Participants received trastuzumab at a loading dose of 8 mg/kg of body weight followed by 6 mg/kg of body weight on Day 1 or Day 2 of each 3-weekly cycle until disease progression, unacceptable toxicity, withdrawal of consent, or death, or the predefined end of study whichever occurred first. Participants also received an aromatase inhibitor (AI), orally as per product labeling (anastrozole: 1 mg once daily or letrozole: 2.5 mg once daily). Participants receiving induction chemotherapy up to the first 18-24 weeks of the treatment period were to receive a taxane (docetaxel every 3 weeks or paclitaxel weekly), administered in line with the respective product labeling.