A Study of Novel Agents or Combinations as Perioperative Treatment in Participants With Locally Advanced Resectable Gastroesophageal Adenocarcinoma

Inclusion Criteria

• Histologically documented gastric, GEJ, or esophageal adenocarcinoma with resectable disease
• Participants who are CLDN18.2-positive and HER2-negative in Sub-study 1 or HER2-positive in Sub-study 2; no specific requirements for Sub-study 3
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• Adequate organ and bone marrow function
• Body weight > 35 kg

Exclusion Criteria

• Participants had any prior anti-cancer treatment or surgery for the current gastric, GEJ, or esophageal cancer.
• Active or prior documented autoimmune or inflammatory disorders requiring systemic treatment with steroids or other immunosuppressive treatment
• Central nervous system (CNS) pathology
• Uncontrolled infections
• Participants with history of (non-infectious) interstitial lung disease (ILD)/pneumonitis, current ILD/pneumonitis, or suspected ILD/pneumonitis
• History of another primary malignancy
• Participants with any known or suspicious distant metastasis
• Uncontrolled hepatitis B and/or chronic or active hepatitis B
• Current or prior use of immunosuppressive medication within 14 days before the first dose of study intervention