• Voluntarily participate in the clinical study; fully understand and are informed about the study and sign the Informed Consent Form (ICF); willing to follow and able to complete all trial procedures.

• Age 18-80 years, gender is not limited.

• Patients with locally advanced unresectable, recurrent unresectable, or metastatic gastric cancer (GC) or gastroesophageal junction cancer (GEJC) confirmed by imaging and other examinations, and histopathologically confirmed as adenocarcinoma.

• Provide a report confirming HER2 overexpression or amplification negativity; defined as IHC 0/1+, or IHC 2+ with FISH/ISH negative.

• No prior systemic therapy for advanced or metastatic GC/GEJC (including anti-HER-2 therapy). Patients who have received adjuvant or neoadjuvant therapy (including chemotherapy, radiotherapy, or chemoradiotherapy) for GC/GEJC are eligible if the time to first recurrence or disease progression is greater than 6 months from the end of the last treatment. Prior use of anti-tumor Traditional Chinese Medicine preparations is allowed but must be discontinued at least 2 weeks before enrollment.

• ECOG performance status score of 0 or 1.

• Must have at least one measurable lesion according to RECIST v1.1 definitions.

• All acute toxicities caused by prior anti-tumor therapy or surgery must have resolved to Grade 0-1 (according to NCI CTCAE v5.0) or to the level specified in the inclusion/exclusion criteria. Alopecia, fatigue, and hearing loss, or other toxicities considered by the investigator not to pose a safety risk to the subject, are excluded.

• Adequate organ function (laboratory tests within 7 days prior to treatment):

‣ Hematology (No blood transfusion, G-CSF use, or drug correction within 14 days prior to screening):

⁃ White blood cell count (WBC) ≥ 3,000/mm³ (3.0 × 10⁹/L);

⁃ Absolute neutrophil count (ANC) ≥ 1,500/mm³ (1.5 × 10⁹/L);

⁃ Platelet count (PLT) ≥ 100,000/mm³ (100 × 10⁹/L);

⁃ Hemoglobin (Hb) ≥ 9.0 g/dL (90 g/L).

• Biochemistry (No albumin transfusion within 14 days prior to screening):

‣ Albumin ≥ 3.0 g/dL (30 g/L);

⁃ Creatinine ≤ 1.5 × Upper Limit of Normal (ULN) or Creatinine Clearance ≥ 50 ml/min (calculated using the Cockcroft-Gault formula);

⁃ Total Bilirubin (BIL) ≤ 1.5 × ULN;

⁃ Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) levels ≤ 2.5 × ULN; for patients with liver metastases, ≤ 5 × ULN.

• Coagulation: International Normalized Ratio (INR) ≤ 1.5, Prothrombin Time (PT), and Activated Partial Thromboplastin Time (APTT) ≤ 1.5 × ULN.

• Urine: Urine protein \< 2+; if urine protein is ≥ 2+, 24-hour urine protein quantification must be ≤ 1g.

• Life expectancy ≥ 3 months.

• Women of childbearing potential must undergo a serum or urine pregnancy test within 7 days before starting treatment, with a negative result, and must not be lactating. All enrolled patients must use adequate barrier contraception throughout the treatment cycle and for 6 months after the end of treatment.