Condition: Advanced/Metastatic Gastroesophageal Adenocarcinoma

The purpose of this study is to assess the efficacy and safety of lenvatinib (E7080/MK-7902) plus pembrolizumab (MK-3475) plus chemotherapy compared with chemotherapy alone in participants with advanced/metastatic gastroesophageal cancer.

The primary study hypotheses are that lenvatinib plus pembrolizumab plus chemotherapy is superior to chemotherapy alone for both overall survival (OS) and progression-free survival (PFS) per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1) as assessed by blinded independent central review (BICR), in participants with programmed cell death-ligand 1 (PD-L1) Combined Positive Score (CPS) ≥1 and in all participants.