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

Inclusion Criteria for Stage 1:

• ECOG Performance Status of 0 or 1
• Inoperable locally advanced, metastatic, or advanced GC or GEJC, with adenocarcinoma confirmed as the predominant histology
• No prior systemic treatment for advanced or metastatic disease
• Life expectancy >= 3 months, as determined by the investigator
• Human epidermal growth factor receptor 2 (HER2)-negative tumors
• Measurable disease according to RECIST v1.1
• Adequate hematologic and end-organ function
• Patients without hepatitis B virus (HBV) infection at screening
• Negative hepatitis C virus (HCV) antibody test at screening, or positive HCV antibody test followed by a negative HCV RNA test at screening
• Negative HIV test at screening
• For women of childbearing potential: agreement to remain abstinent or use contraception, and agreement to refrain from donating eggs, as outlined for each specific treatment arm
• For men: agreement to remain abstinent or use contraception, and agreement to refrain from donating sperm, as outlined for each specific treatment arm

Exclusion Criteria for Stage 1:

• Prior treatment with CD137 agonists or immune checkpoint blockade therapies
• Treatment with investigational therapy within 28 days prior to initiation of study treatment
• Any contraindications to any of the study drugs of the chemotherapy regimen
• Eligible only for the control arm
• Patients with a signet ring cells dominant carcinoma
• Symptomatic, untreated, or actively progressing CNS metastases
• History of leptomeningeal disease
• Active or history of autoimmune disease or immune deficiency
• Significant cardiovascular disease within 3 months prior to initiation of study treatment, unstable arrhythmia, or unstable angina
• History of malignancy other than GC or GEJC within 2 years prior to initiation of study treatment, with the exception of malignancies with a negligible risk of metastasis or death

Exclusion Criteria for Tiragolumab-Containing Arm:

• Prior treatment with an anti-TIGIT agent
• Active Epstein-Barr virus (EBV) infection or known or suspected chronic active EBV infection at screening