This is a Phase II, open-label, multi-drug, multi-centre study designed to assess the efficacy, safety, tolerability, pharmacokinetics, and immunogenicity of novel combination therapies in participants with locally advanced unresectable or metastatic gastric or GEJ adenocarcinoma.

Approximately 360 participants will be assigned across 4 substudies, with approximately 60 evaluable participants of the confirmed recommend dose by SRC for study intervention in each corresponding substudy/cohort.

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).

Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal.

All request will be evaluated as per the AZ disclosure commitment:

https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

Yes, indicates that AZ are accepting requests for IPD, but this does not mean all requests will be shared.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA Pharma Data Sharing Principles. For details of our timelines, please rerefer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

When a request has been approved AstraZeneca will provide access to the deidentified individual patient-level data in an approved sponsored tool . Signed Data Sharing Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information. Additionally, all users will need to accept the terms and conditions of the SAS MSE to gain access. For additional details, please review the Disclosure Statements at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.