The purpose of this study is to assess the effectiveness, safety, and actual treatment status of first-line nivolumab plus chemotherapy in participants with untreated advanced / recurrent gastric cancer in a Japanese real-world setting.

The Time Perspective for this observational study is defined as 'Retrospective and Prospective'.

Inclusion Criteria:

• Histologically confirmed advanced or recurrent gastric cancer
• Have initiated or are confirmed to receive nivolumab plus chemotherapy as the first-line therapy between the date of approval of nivolumab plus chemotherapy and December 31, 2022. For combination chemotherapy, SOX, CapeOX, or FOLFOX is acceptable
• Have signed a written informed consent form of their own free will after they have been given an adequate explanation and a full understanding of this study before enrolling in this study.

Exclusion Criteria:

• Treated with antineoplastic agents as first-line treatment for advanced or recurrent gastric cancer prior to the initiation of nivolumab plus chemotherapy (participants who have received prior perioperative chemotherapy and participants who have received prior bisphosphonates for osseous metastases may be enrolled)
• Confirmed to be positive for HER2
• Diagnosed with gastric cancer and have previously received investigational drugs with anti-tumor effects
• Initiated with nivolumab plus chemotherapy as the first-line treatment for advanced or recurrent gastric cancer at a site other than the study site and were later hospitalized at the study site.
• Judged by the investigators to be inappropriate for enrollment in this study

This study will include participants who received nivolumab plus chemotherapy as first-line treatment for unresectable advanced or recurrent gastric cancer at least once between nivolumab plus chemotherapy approval and December 31, 2022.