A Single-arm, Multicenter Exploratory Clinical Trial of Anlotinib Combined With TQB2450 and the SOX Regimen as First-line Treatment for Advanced Gastric Cancer With Low PD-L1 Expression

Inclusion Criteria: * 1\. Willing and able to provide written informed consent and comply with study procedures. * 2\. Histologically or cytologically confirmed HER2-negative (or HER2 status undetermined) unresectable locally advanced or metastatic gastric/gastroesophageal junction adenocarcinoma (including signet ring cell carcinoma, mucinous adenocarcinoma, and hepatoid adenocarcinoma variants). * 3\. Disease recurrence \>6 months after completion of (neo)adjuvant chemotherapy or radiotherapy. * 4\. At least one measurable or evaluable lesion according to RECIST v1.1 criteria. Measurable lesions must not have received prior local therapy (e.g., radiotherapy); however, lesions within previously irradiated fields may be designated as target lesions if documented progression is demonstrated per RECIST v1.1. * 5\. Age 18-75 years. * 6\. ECOG performance status 0-1. * 7\. Life expectancy ≥3 months. * 8\. Organ Function Requirements and Laboratory Test Criteria During Screening (1) Complete Blood Count (CBC) Criteria： Hemoglobin (Hb): ≥ 90 g/L (no blood transfusion within 14 days) Absolute Neutrophil Count (ANC): ≥ 1.5 × 10⁹/L Platelet Count (PLT): ≥ 100 × 10⁹/L (no use of interleukin-11 \[IL-11\] or thrombopoietin \[TPO\] within 14 days) White Blood Cell Count (WBC): ≥ 4.0 × 10⁹/L (no granulocyte colony-stimulating factor \[G-CSF\] administration within 14 days) (2) Biochemical Panel Requirements: Total Bilirubin (TBIL): ≤ 1.5 × ULN (upper limit of normal),Alanine Aminotransferase (ALT) \& Aspartate Aminotransferase (AST): ≤ 2.5 × ULN,Serum Creatinine (Cr): ≤ 1.5 × ULN or Creatinine Clearance (CrCl): ≥ 60 mL/min (calculated by Cockcroft-Gault formula),Serum Albumin: ≥ 25 g/L (2.5 g/dL) For Subjects with Hepatic Metastases:Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT): ≤ 5 × ULN，White Blood Cell Count (WBC): ≥ 4 × 10⁹/L，Platelet Count (PLT): ≥ 100 × 10⁹/L (without transfusion support)， Absolute Neutrophil Count (ANC): ≥ 1.5 × 10⁹/L (without granulocyte colony-stimulating factor \[G-CSF\] therapy) (3) Cardiac Function Assessment (Echocardiography)：Left Ventricular Ejection Fraction (LVEF): ≥ 50% (or above institutional lower limit of normal) (4) Coagulation Profile：International Normalized Ratio (INR) or Prothrombin Time (PT): ≤ 1.5 × ULN * 9\. Women of reproductive age must use effective contraception during the study period, after the last dose, and for at least 6 months following chemotherapy. It is recommended to start using contraception at least 3 months before the administration of the investigational drug; unsterilized males must also be required to use effective contraception for at least 6 months during the study period, after the last dose, and following chemotherapy. It is recommended to start using contraception at least 3 months before the administration of the investigational drug. * 10\. PD-L1 combined positive score ( CPS) \<5 Exclusion Criteria: * 1\. Prior treatment with anlotinib hydrochloride or any immune checkpoint inhibitors (anti-PD-1, anti-PD-L1, or anti-CTLA-4 antibodies); * 2\. History of immunodeficiency disorders, including HIV infection, other acquired or congenital immunodeficiency diseases, or prior organ transplantation; * 3\. Active hepatitis B or C infection, or active pulmonary tuberculosis; * 4\. CT-confirmed ulcerative lesions or fecal occult blood positivity; * 5\. History of clinically significant bleeding (excluding epistaxis) within 1 month prior to enrollment; * 6\. Previous allogeneic bone marrow or solid organ transplantation; * 7\. Interstitial lung disease including idiopathic pulmonary fibrosis, drug-induced pneumonitis, organizing pneumonia, or CT-confirmed active pneumonia; * 8\. Administration of live attenuated vaccines within 4 weeks before study initiation or anticipated during the study through 5 months post-treatment; * 9\. Systemic corticosteroids (\>10 mg/day prednisone equivalent) or immunosuppressive therapy within 2 weeks prior to study initiation (inhaled or topical corticosteroids are permitted); * 10\. Known symptomatic CNS metastases or leptomeningeal carcinomatosis. Patients with previously treated CNS metastases may be eligible if neurologically stable for ≥4 weeks without steroids or anticonvulsants; * 11\. Conditions impairing oral drug absorption (e.g., dysphagia, chronic diarrhea, or intestinal obstruction); * 12\. Grade ≥2 peripheral neuropathy per NCI CTCAE v5.0; * 13\. Active infections requiring systemic antibiotics within 14 days prior to study entry; * 14\. Hepatic tumor burden exceeding 50% of total liver volume; * 15\. Bone metastases with impending spinal cord compression risk; * 16\. Uncontrolled comorbidities including: * Poorly controlled hypertension (SBP ≥150 mmHg or DBP ≥100 mmHg despite antihypertensives) * Grade ≥2 myocardial ischemia, myocardial infarction, or arrhythmias (QTc ≥480 ms) * NYHA Class III-IV heart failure or LVEF \<50% by echocardiography * Uncontrolled active infections * Decompensated liver cirrhosis or active hepatitis * Uncontrolled diabetes (FBG \>10 mmol/L) * Proteinuria ≥++ on dipstick or confirmed 24-hour urinary protein \>1.0 g * 17\. Non-healing wounds or fractures; * 18\. Coagulopathy (INR \>1.5 or aPTT \>1.5×ULN), bleeding diathesis, or requiring therapeutic anticoagulation: * Known bleeding disorders (hemophilia, coagulopathies) or thrombocytopenia * Hemoptysis (\>2.5 mL/day) within 2 months * Clinically significant bleeding within 3 months (GI bleeding, hemorrhagic ulcers, etc.) * Chronic anticoagulation (warfarin/heparin) or antiplatelet therapy (aspirin ≥300 mg/day or clopidogrel ≥75 mg/day) * 19\. Major surgical procedures within 4 weeks prior to study or anticipated during treatment; * 20\. History within 6 months of: * GI perforation/fistula * Arterial/venous thromboembolism (excluding stable cerebral infarcts) * 21\. Clinically significant pleural/peritoneal effusions requiring intervention (asymptomatic minimal effusions not requiring treatment may be permitted); * 22\. Severe malnutrition; * 23\. Active substance abuse or psychiatric disorders impairing compliance; * 24\. Other active malignancies except: * Curatively treated malignancies with \>2 year disease-free interval * Adequately treated non-melanoma skin cancer or lentigo maligna * Carcinoma in situ with complete resection * 25\. Pregnancy or lactation; * 26\. Any condition deemed by investigators to compromise patient safety or study integrity; * 27\. Participation in other clinical trials within 30 days prior to enrollment or planned during study period.