Novel combinations in participants with locally advanced unresectable or metastatic gastric or gastroesophageal junction adenocarcinoma

Inclusion Criteria

• 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:
• - Participants with HER2-positive (3+ by IHC, or 2+ by IHC and positive by in situhybridisation) or indeterminate gastric or GEJ carcinoma.
• - Untreated or progressive CNS metastatic disease, any leptomeningeal disease, or cord compression.
• - Participants with ascites which cannot be controlled with appropriate interventions.
• - Active infectious diseases, including tuberculosis, HIV infection, or hepatitis B/C.
• - Uncontrolled intercurrent illness.
• - Active or prior documented autoimmune or inflammatory disorders requiring systemic treatment with steroids or other immunosuppressive treatment.
• - History of another primary malignancy.
• - Previous treatment with an immune-oncology agent.
• - Previous treatment with any modalities of Claudin18.2 target therapy or MMAE exposure (when Substudy 3, Substudy 4 is open for recruitment).