This study will be conducted to retrospectively evaluate the treatment patterns in first-line, second-line, and subsequent lines of therapy for HER2-positive Gastric Cancer/Gastroesophageal Junction Cancer (GC/GEJC) patients.

This is a multicenter, non-interventional, retrospective real-world study to analyze the treatment patterns for patients with GC/GEJC in the first-line, second-line, and subsequent lines of treatment. The study will also assess different HER2 sample types, testing methods, and HER2 re-biopsy situations. By evaluating the treatment and testing patterns in clinical practice, this study aims to provide evidence and recommendations for improving the strategies for the treatment and testing of HER2-positive GC/GEJC patients.

Inclusion criteria

• Patients with pathologically diagnosed locally advanced unresectable or metastatic GC/GEJC (limited to those diagnosed since October 1, 2017) and initiating first-line treatment between January 1, 2018, and March 31, 2023
• Patients aged ≥ 18 years at the time of diagnosis with locally advanced unresectable or metastatic GC/GEJC; HER2-positive status2, determined by either tissue samples from the first biopsy or liquid biopsy samples (if a patient has both tissue and liquid biopsy samples, tissue samples will be the standard).

Exclusion criteria

• Patients with other primary malignant tumors
• Patients enrolled in clinical trials and receiving active anti-cancer therapy after July.1, 2017 (excluding retrospective studies).
• Patients with critical missing data in medical records or otherwise deemed for inclusion by the investigator

Patients diagnosed with locally advanced unresectable or metastatic HER2-positive GC/GEJC after October 1, 2017, and initiating first-line therapy between January 1, 2018, and March 31, 2023.