An Open-Label, Multi-Drug, Multi-Centre, Phase II Study to Evaluate the Efficacy, Safety, Tolerability, Pharmacokinetics, and Immunogenicity of Novel Combinations in Participants With Locally Advanced Unresectable or Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma

Inclusion Criteria: * 18 years or older at the time of signing the ICF. * Body weight \> 35 kg. * Previously untreated for unresectable or metastatic gastric or gastroesophageal junction adenocarcinoma. * Has measurable target disease assessed by the Investigator based on RECIST 1.1. * ECOG PS zero or one. * Life expectancy of at least 12 weeks. * Adequate organ and bone marrow function. * Has central lab confirmed Claudin18.2 status at screening from archival tumour collected within past 24 months or from a fresh biopsy when Substudy 3, Substudy 4 i s open for recruitment. Exclusion Criteria…