• Voluntarily enrolled and provided written informed consent;

• Aged 18-70 years (inclusive), male or female;

• Histologically and/or cytologically confirmed unresectable locally advanced or metastatic gastric or gastroesophageal junction adenocarcinoma;

• No prior systemic anticancer therapy;

• HER2 immunohistochemistry (IHC) result of 2+ or 1+, based on either previous test results (confirmed by the investigator) or central laboratory assessment;

• Presence of a single initial unresectable factor;

• At least one measurable lesion per RECIST 1.1;

• Life expectancy ≥ 6 months;

• Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0 or 1;

⁃ Adequate organ function, defined as follows:

‣ Hematological (within 14 days prior to screening, without transfusion or granulocyte colony-stimulating factor \[G-CSF\] support):

• Hemoglobin ≥ 90 g/L;

• Absolute neutrophil count (ANC) ≥ 1.5 × 10⁹/L;

• White blood cell count ≥ 3.0 × 10⁹/L;

• Platelet count ≥ 80 × 10⁹/L;

• Biochemical (within 14 days prior to screening, without albumin infusion):

• Albumin ≥ 28 g/L;

• Total bilirubin ≤ 2 × upper limit of normal (ULN);

• Aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) ≤ 2.5 × ULN in the absence of liver metastases; or ≤ 5 × ULN if liver metastases are present;

• Serum creatinine ≤ 1.5 × ULN; or creatinine clearance (CrCl) ≥ 50 mL/min as calculated by the Cockcroft-Gault formula;

• Coagulation:

• International normalized ratio (INR) or prothrombin time (PT) ≤ 1.5 × ULN;

⁃ Activated partial thromboplastin time (APTT) ≤ 1.5 × ULN.