A Study to Evaluate the Efficacy and Safety of ONO-4538 in Combination With Ipilimumab and Chemotherapy in Chemotherapy-naïve Participants With HER2-negative Unresectable Advanced or Recurrent Gastric Cancer (Including Esophagogastric Junction Cancer)

National Cancer Center Hospital East, Kashiwa-shi

Kanagawa Cancer Center, Yokohama

Osaki Citizen Hospital, Osaki-shi

Osaka University Hospital, Suita-shi

Saitama Medical University International Medical Center, Hidaka-shi

Saitama Cancer Center, Ina-machi, Kitaadati-gun

Shizuoka Cancer Center, Nagaizumi-Cho, Sunto-Gun

University of Tokyo Hospital, Bunkyo-ku

National Cancer Center Hospital, Chuo-ku

Cancer Institute Hospital of JFCR, Koto-ku

IMSUT Hospital, The Institute of Medical Science, The University of Tokyo, Minato-ku

Keio University Hospital, Shinjyuku-ku

Kosin University Gospel Hospital, Busan

Hallym University Sacred Heart Hospital, Anyang-si

National Cancer Center, Goyang-si

CHA Bundang Medical Center, CHA University, Seongnam-si

Seoul National University Bundang Hospital, Seongnam-si

Ajou University Hospital, Suwon

The Catholic University of Korea, St. Vincent's Hospital, Suwon

Kyungpook National University Chilgok Hospital, Daegu

Pusan National University Yangsan Hospital, Yangsan

Jeonbuk national university hospital, Jeonju

Chonnam National University Hwasun Hospital, Hwasun-gun

Chungbuk National University Hospital, Cheongju-si

Dong-A University Hospital, Busan

Inje University Haeundae Paik Hospital, Busan

Pusan National University Hospital, Busan

Keimyung University Dongsan Hospital, Daegu

Chungnam National University Hospital, Daejeon

Konyang University Hospital, Daejeon

Gachon University Gil Medical Center, Incheon

Asan Medical Center, Seoul

Chung-Ang University Hospital, Seoul

Gangnam Severance Hospital, Yonsei University Health System, Seoul

Kangbuk Samsung Hospital, Seoul

Korea University Guro Hospital, Seoul

Samsung Medical Center, Seoul

Seoul National University Hospital, Seoul

Severance Hospital, Yonsei University Health System, Seoul

The Catholic University of Korea, Seoul St. Mary's Hospital, Seoul

Ulsan University Hospital, Ulsan

Kaohsiung Chang Gung Memorial Hospital, Kaohsiung City

Kaohsiung Medical University Chung-Ho Memorial Hospital, Kaohsiung City

Chang Gung Memorial Hospital, Keelung, Keelung

Far Eastern Memorial Hospital, New Taipei City

Taipei Medical University - Shuang Ho Hospital, Ministry of Health and Welfare, New Taipei City

China Medical University Hospital, Taichung

Taichung Veterans General Hospital, Taichung

Chi Mei Hospital, Liouying, Tainan City

National Cheng Kung University Hospital, Tainan City

Koo Foundation Sun Yat-Sen Cancer Center, Taipei

National Taiwan University Hospital, Taipei

Taipei Medical University Hospital, Taipei

Taipei Municipal Wanfang Hospital Managed by Taipei Medical University, Taipei

Taipei Veterans General Hospital, Taipei

Tri-Service General Hospital, Taipei

Chang Gung Memorial Hospital,Linkou, Taoyuan