Conditions: Gastric Cancer
Allocation: RANDOMIZED | Intervention model: PARALLEL
Enrollment: 780
Healthy volunteers: no

Brief summary:
This double-blind, placebo-controlled, randomized, multicenter, international, parallel arm study will evaluate the efficacy and safety of pertuzumab in combination with trastuzumab, fluoropyrimidine and cisplatin as first-line treatment in participants with HER2-positive metastatic gastroesophageal junction (GEJ) or gastric cancer (GC). Participants will be randomized to receive pertuzumab 840 milligrams (mg) or placebo intravenously every 3 weeks (q3w) in combination with trastuzumab (initial dose of 8 milligrams per kilogram \[mg/kg\] intravenously \[IV\] followed by 6 mg/kg IV q3w) and cisplatin and fluoropyrimidine (capecitabine or 5-fluorouracil) for the first 6 treatment cycles. Participants will continue to receive pertuzumab or placebo and trastuzumab until disease progression occurrence of unacceptable toxicity or withdrawal from the study for another reason.

Detailed description:

Arms:
arm 1: Participants will receive pertuzumab in combination with trastuzumab and chemotherapy (cisplatin and fluoropyrimidine \[capecitabine or 5-fluorouracil\]) for the first 6 treatment cycles (cycle length = 21 days). Thereafter, participants will continue to receive pertuzumab and trastuzumab until disease progression, occurrence of unacceptable toxicity, or withdrawal from the study for another reason. arm 2: Participants will receive placebo in combination with trastuzumab and chemotherapy (cisplatin and fluoropyrimidine \[capecitabine or 5-fluorouracil\]) for the first 6 treatment cycles (cycle length = 21 days). Thereafter, participants will continue to receive placebo and trastuzumab until disease progression, occurrence of unacceptable toxicity, or withdrawal from the study for another reason.

Interventions: intervention 1: 5-Fluorouracil intervention 2: Capecitabine intervention 3: Cisplatin intervention 4: Pertuzumab intervention 5: Placebo intervention 6: Trastuzumab
Intervention descriptions: intervention 1: Participants will receive 5-fluorouracil 800 milligrams per meter square (mg/m\^2)/24 hour IV infusion for 120 hours (Days 1-5) q3w for 6 cycles. intervention 2: Participants will receive capecitabine 1000 mg/m\^2 orally twice daily, evening of Day 1 to morning of Day 15 (28 doses) q3w for 6 cycles. intervention 3: Participants will receive cisplatin 80 mg/m\^2 IV q3w for 6 cycles. intervention 4: Participants will receive pertuzumab 840 mg IV q3w until disease progression, occurrence of unacceptable toxicity, or withdrawal from the study for another reason. intervention 5: Participants will receive placebo (matched to pertuzumab) IV q3w until disease progression, occurrence of unacceptable toxicity, or withdrawal from the study for another reason. intervention 6: Participants will receive 8 mg/kg IV initial dose on Day 1, followed by 6 mg/kg IV q3w until disease progression, occurrence of unacceptable toxicity, or withdrawal from the study for another reason.

Protocol document: