Neoadjuvant Apatinib Combined With Sintilimab and Perioperative SOX Versus Neoadjuvant Sintilimab Combined With Perioperative SOX for Intestinal Type of Locally Advanced Gastric/Gastroesophageal Junction Adenocarcinoma

This study aims to compare the efficacy and safety of neoadjuvant apatinib combined with sintilimab and perioperative SOX chemotherapy versus neoadjuvant sintilimab combined with perioperative SOX chemotherapy in locally advanced intestinal-type gastric cancer/gastroesophageal junction adenocarcinoma. The primary questions include: 1. Whether the complete remission rate (pCR) of the apatinib combined with sintilimab and SOX regimen is higher than that of the sintilimab combined with SOX regimen. 2. The safety of the apatinib combined with sintilimab and SOX regimen. Participants will be divided into: 1. Experimental Group: Participants will receive an intravenous injection of sintilimab (200 mg) combined with the SOX regimen (oxaliplatin 130 mg/m² and S-1, with the initial dose determined based on body surface area). Additionally, apatinib (250 mg) will be administered orally once daily during the first three neoadjuvant cycles. 2. Control Group: Participants will receive treatment with the sintilimab combined with the SOX regimen. This treatment will be administered for three to four cycles prior to surgery, followed by radical surgery, including D2 or D2+ lymph node dissection. Surgery is scheduled four weeks after the last neoadjuvant therapy (NAT) cycle. Within 3 to 6 weeks post-surgery, patients will begin adjuvant SOX chemotherapy. Postoperative patients will receive four cycles of adjuvant SOX chemotherapy, administered every three weeks.