Substudy 06C: A Study of Investigational Agents With Pembrolizumab (MK-3475) and Chemotherapy in Participants With First-Line Locally Advanced Unresectable/Metastatic Gastroesophageal Adenocarcinoma (MK-3475-06C/KEYMAKER-U06)

University of Arizona Cancer Center-University of Arizona Cancer Center ( Site 6927), Tucson, Arizona, United States

UCLA Hematology/Oncology - Santa Monica ( Site 6905), Los Angeles, California, United States

Norton Hospital-Norton Cancer Institute - Downtown ( Site 6900), Louisville, Kentucky, United States

The Cancer and Hematology Centers ( Site 6912), Grand Rapids, Michigan, United States

Hematology-Oncology Associates of Central NY, P.C. ( Site 6925), East Syracuse, New York, United States

Columbia University Irving Medical Center-CUIMC Herbert Irving Comprehensive Cancer Center Clinical ( Site 6907), New York, New York, United States

UPMC Hillman Cancer Center-UPMC ( Site 6904), Pittsburgh, Pennsylvania, United States

University of Texas MD Anderson Cancer Center ( Site 6920), Houston, Texas, United States

Liga Norte Riograndense Contra o Câncer ( Site 6303), Natal, Rio Grande do Norte, Brazil

Hospital Nossa Senhora da Conceição ( Site 6301), Porto Alegre, Rio Grande do Sul, Brazil

ICESP - INSTITUTO DO CÂNCER DO ESTADO DE SÃO PAULO ( Site 6300), São Paulo, Brazil

IBCC - Instituto Brasileiro de Controle do Câncer ( Site 6304), São Paulo, Brazil

Clínica Puerto Montt ( Site 6409), Port Montt, Los Lagos Region, Chile

Centro de Investigación del Maule ( Site 6408), Talca, Maule Region, Chile

FALP-UIDO ( Site 6400), Santiago, Region M. de Santiago, Chile

Centro de Oncología de Precisión-Oncology ( Site 6404), Santiago, Region M. de Santiago, Chile

Clínica UC San Carlos de Apoquindo ( Site 6405), Santiago, Region M. de Santiago, Chile

Bradfordhill-Clinical Area ( Site 6401), Santiago, Region M. de Santiago, Chile

Bradford Hill Norte ( Site 6407), Antofagasta, Chile

Beijing Cancer hospital-Digestive Oncology ( Site 5500), Beijing, Beijing Municipality, China

The 900th Hospital of the Joint Logistics Support Force of the Chinese People's Liberation Army ( Site 5501), Fuzhou, Fujian, China

The First Affiliated hospital of Xiamen University ( Site 5503), Xiamen, Fujian, China

Henan Cancer Hospital ( Site 5504), Zhengzhou, Henan, China

The First Affiliated Hospital of Nanchang University ( Site 5514), Nanchang, Jiangxi, China

Fudan University Shanghai Cancer Center ( Site 5513), Shanghai, Shanghai Municipality, China

Xinjiang Medical University Cancer Hospital - Urumqi ( Site 5506), Ürümqi, Xinjiang, China

Sir Run Run Shaw Hospital of Zhejiang University School of Medicine ( Site 5510), Hangzhou, Zhejiang, China

CHU-BREST Cavale Blanche ( Site 5104), Brest, Finistere, France

CIC. ( Site 5100), Lille, Nord, France

Pitie Salpetriere University Hospital-Hepato-Gastro-Enterology ( Site 5102), Paris, Île-de-France Region, France

NCT-Department of Medical Oncology ( Site 6809), Heidelberg, Baden-Wurttemberg, Germany

Universitaetsklinikum Duesseldorf-Gastroenterology, Hepatology and Infectiology ( Site 6802), Düsseldorf, North Rhine-Westphalia, Germany

Universitaetsklinikum Carl Gustav Carus Dresden-Medical Dept I - Medical Oncology ( Site 6806), Dresden, Saxony, Germany

Facharztzentrum Eppendorf-Facharztzentrum Eppendorf ( Site 6807), Hamburg, Germany

IRCCS - Istituto Romagnolo per lo Studio dei Tumori (IRST) "Dino Amadori"-Oncologia Medica ( Site 5207), Meldola, Emilia-Romagna, Italy

Fondazione IRCCS Istituto Nazionale dei Tumori-Struttura Complessa Oncologia Medica 1 ( Site 5200), Milan, Lombardy, Italy

Azienda Ospedaliero Universitaria Pisana ( Site 5206), Pisa, Tuscany, Italy

Ospedale San Raffaele-Oncologia Medica ( Site 5202), Milan, Italy

Oslo universitetssykehus, Radiumhospitalet ( Site 6501), Oslo, Norway

Asan Medical Center-Department of Oncology ( Site 5901), Seoul, South Korea

Samsung Medical Center-Division of Hematology/Oncology ( Site 5900), Seoul, South Korea

Hôpitaux Universitaires de Genève (HUG) ( Site 6701), Geneva, Canton of Geneva, Switzerland

Kantonsspital Graubünden-Medizin ( Site 6700), Chur, Kanton Graubünden, Switzerland

China Medical University Hospital ( Site 6007), Taichung, Taiwan

National Cheng Kung University Hospital ( Site 6001), Tainan, Taiwan

National Taiwan University Hospital-Oncology ( Site 6000), Taipei, Taiwan

Taipei Veterans General Hospital ( Site 6005), Taipei, Taiwan

Faculty of Medicine Siriraj Hospital ( Site 6102), Bangkoknoi, Bangkok, Thailand

Chulalongkorn Hospital ( Site 6104), Pathumwan, Bangkok, Thailand

Ramathibodi Hospital ( Site 6103), Ratchathewi, Bangkok, Thailand

Songklanagarind hospital ( Site 6101), Hat Yai, Changwat Songkhla, Thailand