This study is a multicenter non-interventional observational retrospective study with secondary data collection

It will be multicenter study. Planned number of study sites is about 50 oncological centers specialized on anticancer chemotherapy in various regions of Russia. A multi-center collaborative effort will help to describe characteristics of patients with HER2-positive gastric and/or GEJ adenocarcinoma in different regions in the most comprehensive way and to capture more patients into database, not only limited to a single institution

Inclusion Criteria:

• Patients with locally advanced/metastatic gastric and/or gastroesophageal junction (GEJ) adenocarcinoma, with the diagnosis established between the 1st January 2022 and the 1st January 2023.
• Patients with documented HER2+ status based on IHC score ± ISH status.
• Patients have an adequate archival tumor sample and slides suitable for reassessment HER2 status by the reference laboratory.
• Age ≥ 18 years at the time of inclusion.
• Patients provided written consent allowing for data and samples to be used in the future and this study would be covered by the consent for future use in accordance with ICH GCP, GPP (Good Pharmacoepidemiology Practices) and local law prior to inclusion in the study. If the patient is deceased, a waiver may be accepted.

Exclusion Criteria:

• Patients receiving trastuzumab deruxtecan currently or in the anamnesis.
• The participation in any randomized controlled trial within period since diagnosis (between the 1st January 2022 and the 1st January 2023) until the timepoint of data collection

300 adult patients with HER2-positive locally advanced/metastatic gastric and/or gastroesophageal junction cancer who are monitored and treated