• Patients with histologically confirmed gastric or gastroesophageal junction adenocarcinoma who have not received prior anti-tumor therapy for gastric/gastroesophageal junction cancer.

• Age: ≥18 and ≤70 years, both male and female.

• Ability to provide fresh tumor tissue (preferred) or archival formalin-fixed paraffin-embedded (FFPE) tumor blocks/unstained slides obtained within 6 months before enrollment.

• Availability of biomarker testing results before enrollment.

• ECOG performance status of 0-1.

• Life expectancy ≥ 6 months.

• Adequate organ and bone marrow function.

• Female participants must be either non-childbearing potential or of childbearing potential with a negative serum pregnancy test within 3 days prior to treatment initiation and not lactating. Childbearing-potential participants and their partners must agree to avoid sperm/ovum donation and comply with contraception requirements from informed consent signing until 8 months after the last dose.

• Voluntarily signed informed consent form, with willingness and ability to comply with scheduled visits, treatments, laboratory tests, and study procedures.