An Umbrella Study Evaluating the Efficacy and Safety of Multiple Treatment Combinations in Patients With Gastric or Gastroesophageal Junction Carcinoma

This is a Phase Ib/II, open-label, multicenter, randomized umbrella study in participants with advanced gastric carcinoma (GC) or gastroesophageal junction carcinoma (GEJC). The study is designed with the flexibility to open new treatment arms as new treatments become available, close existing treatment arms that demonstrate minimal clinical activity or unacceptable toxicity, and modify the participant population. Cohort 1 will enroll participants with inoperable locally advanced, metastatic, or advanced GC or GEJC, with adenocarcinoma confirmed as the predominant histology, who have not received prior systemic therapy for advanced or metastatic disease. Eligible participants will initially be randomly assigned to one of treatment arms (Stage 1). Participants who experience loss of clinical benefit or unacceptable toxicity during Stage 1 may be eligible to receive treatment with a different treatment combination (Stage 2). When a Stage 2 treatment combination is available, this will be introduced by amending the protocol.