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

Study Design: This is a prospective, single-center, single-arm, open-label Phase II clinical study. The study aims to evaluate the efficacy and safety of Adebrelimab combined with Apatinib and SOX regimen as conversion therapy for patients with advanced, unresectable gastric or gastroesophageal junction (GEJ) adenocarcinoma. The study plans to enroll approximately 49 participants who are assessed by investigators as having conversion therapy potential (defined as single organ metastasis, retroperitoneal lymph node metastasis, supraclavicular lymph node metastasis, limited peritoneal metastasis, or invasion of surrounding organs). Treatment Protocol: Eligible participants will receive a four-drug combination therapy consisting of Adebrelimab, Apatinib Mesylate, Oxaliplatin, and S-1. The treatment is administered in 3-week cycles: Adebrelimab: 1200 mg, intravenous infusion on Day 1. Apatinib Mesylate: 250 mg, oral, once daily. Oxaliplatin: 130 mg/m², intravenous infusion on Day 1. S-1 (Tegafur, Gimeracil, and Oteracil Potassium): 40-60 mg (based on Body Surface Area), oral, twice daily on Days 1-14. Study Procedures and Phases: Conversion Treatment Phase: Patients will receive treatment for a minimum of 2 cycles and a maximum of 8 cycles. Resectability will be assessed by the investigator every 2 cycles using imaging evaluation. Surgical Intervention: If the tumor is assessed as resectable: Apatinib will be discontinued for one cycle prior to the planned surgery to ensure safety. Surgery should be performed between 3 to 6 weeks (maximum 6 weeks) after the last dose of the study drug. Post-operative Phase: The decision to administer adjuvant therapy will be made by the investigator based on post-operative pathological results. If adjuvant therapy is required, it will commence at least 4 weeks but no later than 10 weeks after surgery. Maintenance Phase: If the tumor remains unresectable after 8 cycles of combination therapy, the patient will transition to a maintenance phase. The specific treatment regimen during the maintenance phase will be determined by the investigator based on the patient's condition. Follow-up: Upon discontinuation of treatment, patients will undergo safety follow-ups every 30 days until 90 days after the last dose. Subsequently, patients will enter the survival follow-up period to monitor disease recurrence, metastasis, and overall survival. Follow-ups will occur every 3 months for the first 2 years and every 6 months for years 2 to 5.