Clinical Efficacy of Adebrelimab With or Without Apatinib Mesilate and SOX Neoadjuvant Therapy in Locally Advanced Gastric Cancer

Inclusion criteria

**Inclusion Criteria** 1. Age 18-75 years (inclusive). 2. Histologically or cytologically confirmed unresectable, locally advanced or metastatic HER2-negative adenocarcinoma of the stomach or gastro-oesophageal junction (GEJ).

• No prior systemic chemotherapy, radiotherapy, targeted therapy, or immunotherapy for advanced disease. Subjects who have received prior (neo)adjuvant chemotherapy and/or radiotherapy are eligible provided the last dose was completed ≥ 6 months before randomisation.

• At least one measurable lesion per RECIST 1.1 (see Appendix 2). 5. Eastern Cooperative Oncology Group performance status (ECOG PS) 0-1 (see Appendix 4).

• Estimated life expectancy > 3 months. 7. Adequate major organ function defined as:

• Haematology (obtained ≤ 14 days without transfusion):

• Hb ≥ 80 g/L
• WBC ≥ 3 × 10⁹/L
• ANC ≥ 1.5 × 10⁹/L
• PLT ≥ 100 × 10⁹/L
• Biochemistry:

• Total bilirubin < 1.5 × upper limit of normal (ULN)
• ALT and AST < 2.5 × ULN; ALP ≤ 1.5 × ULN
• Serum creatinine ≤ 1 × ULN and calculated creatinine clearance ≥ 60 mL/min (Cockcroft-Gault formula) 8. Women of child-bearing potential must have a negative serum pregnancy test within 7 days prior to enrolment and must use highly effective contraception from screening until 8 weeks after the last dose of study drug. Men must be surgically sterile or agree to use effective contraception during the same period.

• No participation in any other interventional clinical trial during the pre-treatment or on-treatment phases of this study.

• Voluntary written informed consent obtained; willing and able to comply with study procedures and follow-up.

Exclusion criteria

Exclusion criteria

Subjects meeting any of the following conditions will be excluded from enrollment:

• Known or suspected hypersensitivity to the investigational drug or any drug of the same class.
• Other malignancies within the past 5 years, except adequately treated basal-cell or squamous-cell carcinoma of the skin or carcinoma in situ of the cervix.
• Currently receiving treatment in another interventional clinical trial, or any systemic anti-gastric-cancer therapy within 4 weeks prior to the first dose.
• Systemic Chinese patent medicines with anti-tumor indications or immunomodulatory agents (e.g., thymosin, interferon, interleukins; local intrapleural use for effusion control is permitted) received within 2 weeks before the first dose.
• Prior exposure to: anti-PD-1, anti-PD-L1, anti-PD-L2, or any agent targeting other T-cell co-stimulatory or co-inhibitory pathways (including but not limited to CTLA-4, OX-40, CD137); or prior chemotherapy including S-1.
• Live-vaccine administration within 4 weeks before enrollment or planned during the study.

Note: Inactivated seasonal influenza vaccine by injection is allowed within 4 weeks; intranasal live-attenuated influenza vaccine is prohibited.

• Active autoimmune disease requiring systemic therapy (e.g., immunosuppressants, corticosteroids, or disease-modifying agents) within 2 years before the first dose. Replacement therapy (thyroxine, insulin, physiologic glucocorticoids for adrenal or pituitary insufficiency) is not considered systemic therapy.
• Prior allogeneic bone-marrow or solid-organ transplantation.
• Any condition that could impair drug absorption or inability to swallow oral medication.
• Uncontrolled hypertension despite optimal medical management:

• SBP ≥ 150 mmHg or DBP ≥ 100 mmHg on a single antihypertensive, or requirement of ≥ 2 antihypertensive agents.
• Urinalysis showing proteinuria ≥ 2+ and 24-h urinary protein > 1.0 g.
• Active gastro-duodenal ulcer, ulcerative colitis, or other gastrointestinal disorders with bleeding risk; un-resected tumors with active hemorrhage; or any other condition judged by the investigator to predispose to GI bleeding or perforation.
• Significant bleeding tendency within 3 months before enrollment: overt bleeding > 30 mL, hematemesis, melena, hematochezia; hemoptysis (> 5 mL fresh blood within 4 weeks); or thrombo-embolic event (including stroke/TIA) within 12 months.
• Clinically significant cardiovascular disease:

• Acute MI, unstable/severe angina, or CABG within 6 months before enrollment;
• NYHA class > II congestive heart failure;
• Ventricular arrhythmia requiring therapy;
• QTc ≥ 480 ms on baseline ECG.
• Active or uncontrolled severe infection (≥ CTCAE grade 2).
• Known HIV infection; clinically significant hepatic disorders:

• Chronic hepatitis B with active replication (HBV DNA > 1 × 10⁴ copies/mL or > 2000 IU/mL);
• Hepatitis C with detectable HCV RNA (> 1 × 10³ copies/mL);
• Other hepatitis or cirrhosis.
• Known dihydropyrimidine dehydrogenase (DPD) deficiency.
• Any condition that, in the opinion of the investigator, would compromise the subject's safety or interfere with study participation.