Adebrelimab Plus Apatinib Combined With SOX Regimen as Conversion Therapy for Gastric Cancer

Inclusion Criteria:

* Age 18-75 years at the time of enrollment, with an estimated life expectancy of ≥ 3 months.
* Histologically or cytologically confirmed gastric cancer or gastroesophageal junction cancer, predominantly adenocarcinoma.
* Unresectable locally advanced gastric or gastroesophageal junction adenocarcinoma (Stage III or IV), as determined by the investigator based on CT, MRI, and/or PET-CT.
* Disease with conversion (translational) therapeutic potential, as assessed by the investigator.
* No prior anti-tumor treatment, including chemotherapy, radiotherapy, targeted therapy, immunotherapy, or other systemic anticancer therapies.
* Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
* Adequate hematologic function within 14 days prior to enrollment:

  * White blood cell count ≥ 3.5 × 10⁹/L.
  * Absolute neutrophil count ≥ 1.5 × 10⁹/L.
  * Hemoglobin ≥ 90 g/L (9.0 g/dL).
  * Platelet count ≥ 100 × 10⁹/L.
  * Adequate hepatic function within 14 days prior to enrollment:Total bilirubin ≤ 1.5 × upper limit of normal (ULN);ALT and AST ≤ 2.5 × ULN in patients without liver metastases;ALT and AST ≤ 5 × ULN in patients with liver metastases;Adequate renal function:Serum creatinine ≤ 1.5 × ULN;Women of childbearing potential must have a negative serum or urine pregnancy test within 7 days prior to enrollment and agree to use effective contraception during the study and for at least 12 weeks after the last dose.
* Male participants must be surgically sterile or agree to use effective contraception during the study and for at least 12 weeks after the last dose
* Ability to understand and willingness to sign a written informed consent form
* Expected to comply with study procedures and follow-up requirements

Exclusion Criteria:

* HER2-positive gastric or gastroesophageal junction adenocarcinoma.
* Conditions that may significantly affect oral drug absorption, including inability to swallow, persistent nausea or vomiting, chronic diarrhea, or intestinal obstruction.
* Known hypersensitivity or allergy to adebrelimab, apatinib, oxaliplatin, S-1 (tegafur/gimeracil/oteracil), or any of their excipients.
* History of severe allergic reactions to monoclonal antibodies.
* Active autoimmune disease or autoimmune disorders requiring systemic treatment.
* Congenital or acquired immunodeficiency.
* Use of systemic immunosuppressive therapy within 14 days prior to the first dose of study treatment.
* Administration of live attenuated vaccines within 4 weeks prior to the first dose or planned during the study period.
* Severe infection within 4 weeks prior to initiation of study treatment.
* History of allogeneic organ transplantation or allogeneic hematopoietic stem cell transplantation.
* Evidence of interstitial lung disease, including pulmonary fibrosis, interstitial pneumonia, pneumoconiosis, radiation pneumonitis, drug-induced pneumonitis, or severely impaired pulmonary function.
* Uncontrolled hypertension despite at least 3 months of antihypertensive treatment.
* Uncontrolled clinically significant cardiovascular disease.
* High risk of severe bleeding, as judged by the investigator.
* Peripheral neuropathy of Grade \> 2 according to CTCAE.
* Participation in another interventional clinical trial within 4 weeks prior to enrollment or within 5 half-lives of the investigational product, whichever is longer.
* Any condition that, in the investigator's judgment, makes the participant unsuitable for study participation.