This phase II trial is a single-arm and single-center clinical study. Neoadjuvant chemotherapy is a standard treatment for locally advanced gastric cancer. The SOX regimen has became the standard perioperative chemotherapy regimen for locally advanced gastric cancer. For HER2-positive locally advanced gastric cancer, the neoadjuvant treatment is still based on chemotherapy alone. Some phase II studies have shown that chemotherapy combined with trastuzumab can further improve the pathological response. But it has not yet become a standard treatment strategy.~In the field of gastric cancer, checkpoint inhibitors have become a standard treatment for advanced or metastatic gastric cancer. PD-1 monoclonal antibody (Sintilimab) + trastuzumab + chemotherapy (SOX regimen ) may be an ideal perioperative treatment for HER2-positive locally advanced gastric cancer.
The SOX regimen has became the standard perioperative chemotherapy for locally advanced gastric cancer; The immune checkpoint inhibitors have become a standard treatment for advanced or metastatic gastric cancer；For HER2-positive locally advanced gastric cancer, some phase II studies have shown that chemotherapy combined with trastuzumab can further improve the pathological remission rate;This prospective phase II clinical trial was designed, using SOX combined with sintilimab and trastuzumab to treat HER2 positive locally advanced gastric or gastroesophageal junction adenocarcinoma patients.