A Safety and Efficacy Study of Treatment Combinations With and Without Chemotherapy in Adult Participants With Advanced Upper Gastrointestinal Tract Malignancies

Key Inclusion Criteria:

• Participants with histologically confirmed diagnosis of locally advancedunresectable or metastatic gastric, GEJ, or esophageal adenocarcinoma with lifeexpectancy ≥3 months as assessed by the Investigator

• Eastern cooperative oncology group (ECOG) Performance Score of 0-1

• At least one measurable target lesion per RECIST v1.1.

• Adequate organ and marrow function

• Able to provide an archival tumor sample that is representative of the cancer underinvestigation and suitable for central PD-L1 testing

Key Exclusion Criteria:

• Participants with underlying medical conditions that, in the Investigator's orSponsor's opinion, will make the administration of investigational productshazardous

• Only for Cohort A: Known Human Epidermal Growth Factor Receptor 2 (HER-2) positivetumor

• Known untreated, symptomatic, or actively progressing central nervous system (brain)metastases. Participants with leptomeningeal metastases are excluded fromenrollment.

• Discontinued use of prior immune checkpoint therapy due to immune related adverseevents; received prior treatment with an anti-TIGIT monoclonal antibody.

• History of trauma or major surgery within 28 days prior to enrollment.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.