Establishment of Precision Targeted Therapy Strategies for Advanced Gastric Cancer Based on Novel Molecular Subtyping

Inclusion Criteria: 1. Age ≥18 years, regardless of gender; 2. Histologically or pathologically confirmed gastric adenocarcinoma or adenocarcinoma of the gastroesophageal junction; 3. Advanced or metastatic disease with no prior systemic therapy for advanced-stage disease (Patients who relapsed \>6 months after completing neoadjuvant/adjuvant therapy are eligible, with prior neoadjuvant/adjuvant regimens not counted as prior lines of therapy); 4. At least one measurable lesion per Response Evaluation Criteria in Solid Tumors (RECIST v1.1); 5. Archival or fresh tumor tissue sample available for biomarker testing (HER2, CLDN18.2, and PD-L1 expression); 6. ECOG performance status: 0-1; 7. Life expectancy ≥12 weeks; 8. Adequate organ and bone marrow function meeting the following criteria: 1. Hemoglobin ≥90 g/L (no blood transfusion within 14 days); 2. Absolute neutrophil count (ANC) ≥1.5×10⁹/L; 3. Platelet count ≥90×10⁹/L; 4. Total bilirubin ≤1.5×upper limit of normal (ULN); 5. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5×ULN (≤5×ULN if liver metastases are present); 6. Serum creatinine ≤1.5×ULN; 7. Left ventricular ejection fraction (LVEF) ≥50% by echocardiography; QTc interval \<450 ms for males and \<470 ms for females; 9. Coagulation parameters: 10. For patients not on anticoagulation therapy: INR ≤1.5 and activated partial thromboplastin time (APTT) ≤1.5×ULN; 11. For patients receiving full-dose or parenteral anticoagulation: Stable anticoagulant dose for ≥2 weeks prior to enrollment, with coagulation tests within the therapeutic range; 12. Contraception requirements: 13. Women of childbearing potential must have a negative pregnancy test (serum or urine) within 14 days prior to enrollment and agree to use effective contraception during the study and for 3 months after the last dose; 14. Men must be surgically sterile or agree to use effective contraception during the study and for 3 months after the last dose; 15. Recovery from prior therapy-related toxicities to ≤Grade 1 (surgical wounds must be fully healed if applicable); 16. Voluntary participation with signed informed consent form and anticipated adherence to protocol requirements. Exclusion Criteria: 1. History of gastrointestinal perforation and/or fistula within 6 months prior to treatment, or active gastrointestinal bleeding within 3 months; 2. Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage; 3. Known history of hypersensitivity to any component of the investigational drug(s) or excipients; 4. Prior treatments meeting any of the following: 1. Received any investigational drug within 4 weeks prior to the first dose of the study drug or within 5 half-lives of the last investigational agent (whichever is shorter); 2. Concurrent enrollment in another interventional clinical study (observational or follow-up studies are permitted); 3. Received antitumor therapy (including radiotherapy, chemotherapy, immunotherapy, endocrine therapy, targeted therapy, biologics, or tumor embolization) within 2 weeks prior to the first dose of the study drug; 5. History of leptomeningeal metastasis or current active brain metastases; 6. Severe infection (CTCAE v5.0 Grade \>2) within 4 weeks prior to the first dose of the study drug (e.g., pneumonia requiring hospitalization, bacteremia, or septic complications); active pulmonary inflammation on baseline chest imaging, or signs/symptoms of infection requiring oral/IV antibiotics within 2 weeks prior to the first dose (prophylactic antibiotics excluded); 7. History of interstitial lung disease (except radiation pneumonitis without steroid treatment or non-infectious pneumonitis); 8. Active tuberculosis (TB) infection confirmed by medical history or CT scan, history of active TB within 1 year prior to enrollment, or untreated active TB diagnosed \>1 year prior to enrollment; 9. Diagnosis of another malignancy within 5 years prior to the first dose of the study drug, except malignancies with low metastatic/lethal risk (5-year survival rate \>90%), such as adequately treated basal cell carcinoma, squamous cell skin cancer, or carcinoma in situ of the cervix; 10. Pregnant or lactating women; 11. Other conditions deemed by the investigator to jeopardize subject safety or trial integrity, including severe comorbidities (e.g., psychiatric disorders), clinically significant laboratory abnormalities, or social/family factors that may compromise protocol adherence or data collection.