A Study to Evaluate the Efficacy and Safety of ONO-4538 in Combination With Ipilimumab and Chemotherapy in Chemotherapy-naïve Participants With HER2-negative Unresectable Advanced or Recurrent Gastric Cancer (Including Esophagogastric Junction Cancer)

A Randomized, Multicenter, Open-label, Phase III Study to Compare the Efficacy and Safety of ONO-4538 in Combination With Ipilimumab, Fluoropyrimidine-based and Platinum-based Chemotherapy (Hereinafter Referred to as "Chemotherapy") Versus Chemotherapy in Chemotherapy-naïve Participants With Human Epidermal Growth Factor Receptor 2 (HER2)-Negative Unresectable Advanced or Recurrent Gastric Cancer (Including Esophagogastric Junction Cancer)

This study is to compare and evaluate the efficacy and safety of ONO-4538 in combination with ipilimumab and chemotherapy versus chemotherapy in chemotherapy-naïve participants with HER2-negative unresectable advanced or recurrent gastric cancer (including esophagogastric junction cancer).

Inclusion Criteria:

1. Participants with unresectable advanced or recurrent gastric cancer (including esophagogastric junction cancer) that has been histologically confirmed to be predominant adenocarcinoma
2. Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) score 0 or 1
3. Participants who have a life expectancy of at least 3 months

Exclusion Criteria:

1. Participants with a history or complications of multiple cancers
2. Participants with a complication or history of severe hypersensitivity to any other antibody products
3. Participants with concurrent autoimmune disease or a history of chronic or recurrent autoimmune disease.