HELOISE: Phase IIIb Randomized Multicenter Study Comparing Standard-of-Care and Higher-Dose Trastuzumab Regimens Combined With Chemotherapy as First-Line Therapy in Patients With Human Epidermal Growth Factor Receptor 2–Positive Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma

PurposeTo compare standard-of-care (SoC) trastuzumab plus chemotherapy with higher-dose (HD) trastuzumab plus chemotherapy to investigate whether HD trastuzumab increases trastuzumab serum trough concentration (Ctrough) levels and increases overall survival (OS) in first-line human epidermal growth factor receptor 2–positive metastatic gastric or gastroesophageal junction adenocarcinoma.Patients and MethodsPatients with Eastern Cooperative Oncology Group performance status 2, no prior gastrectomy, and ≥ two metastatic sites were randomly assigned at a one-to-one ratio to loading-dose trastuzumab 8 mg/kg followed by SoC trastuzumab maintenance 6 mg/kg every 3 weeks or loading-dose trastuzumab 8 mg/kg followed by HD trastuzumab maintenance 10 mg/kg every 3 weeks until progression; treatment in each arm was combined with cisplatin 80 mg/m2 plus capecitabine 800 mg/m2 twice per day in cycles 1 to 6. The primary objective was HD trastuzumab OS superiority (all randomly assigned patients [full-analysis set]). F...