A Study to Compare Pertuzumab + Trastuzumab + Vinorelbine vs. Placebo + Trastuzumab + Docetaxel in Previously Untreated HER2-positive Metastatic Breast Cancer

"administered as combined therapy with pertuzumab and vinorelbine or docetaxel.~Trastuzumab will be administered as an IV loading dose of 8 milligrams per kilogram (mg/kg) on day 1 of cycle 1 (1 cycle length = 21 days), and 6 mg/kg Q3W on day 1 of subsequent cycles until progressive disease, intolerable toxicity, or death."

"administered as combined therapy with Kanjinti® and vinorelbine or docetaxel.~Pertuzumab will be administered as an IV loading dose of 840 milligrams (mg) on day 1 of cycle 1 (1 cycle length = 21 days), and 420 mg Q3W on day 1 of subsequent cycles until progressive disease, intolerable toxicity, or death."

"administered as combined therapy with Kanjinti® and pertuzumab.~Vinorelbine will be administered as an IV dose of 25 milligrams per kilogram (mg/kg) on days 1 and 8 of cycle 1 (1 cycle length = 21 days), and 25mg/kg up to 30 mg/kg (as per treating physician discretion) Q3W on day 1 of subsequent cycles until progressive disease, intolerable toxicity, or death."

"administered as combined therapy with Kanjinti® and pertuzumab.~Docetaxel will be administered as an IV dose of 75 milligrams per square meter (mg/m\^2) on day 1 of cycle 1 (1 cycle length = 21 days), and 75 mg/m\^2 (up to 100 mg/m\^2 as per treating physician discretion) Q3W on day 1 of subsequent cycles until progressive disease, intolerable toxicity, or death."