Neoadjuvant chemotherapy and neoadjuvant radiotherapy and chemotherapy can not only improve the surgical resection rate and postoperative pathological remission rate, but also prolong the postoperative recurrence-free survival and benefit patients.Recent studies have confirmed that immume point inhibitors PD-1 and CTLA-4 monoclonal antibody have a certain effect in advanced gastric and gastroesophageal junction adenocarcinoma which had experienced multi-line treatment. Furthermore，the FOLFOX protocol is recommended as a new adjuvant treatment for locally advanced gastric cancer.In order to further improve the surgical resection rate and survival rate by improving the efficacy of neoadjuvant therapy for locally advanced gastric and gastroesophageal junction adenocarcinoma, the investigators selected PD-1 monoclonal antibody combined with FOLFOX neoadjuvant therapy for locally advanced gastric and gastroesophageal junctions Adenocarcinoma.The aim of this study is to observe the efficacy, safety, postoperative pathological response rate and survival benefit of immume checkpoint inhibitor PD-1 SHR1210 combined with chemotherapy in neoadjuvant therapy of locally advanced resectable gastric and gastroesophageal junction adenocarcinoma. In addition ，the investigators will explore the relationship between the immunophenotype of gastric cancer and the efficacy and drug resistance of immunotherapy combined with chemotherapy, and screen out biomarkers that can predict the efficacy of immunotherapy.
The aim of this study is to observe the efficacy, safety, postoperative pathological response rate and survival benefit of immume checkpoint inhibitor PD-1 SHR1210 combined with chemotherapy in neoadjuvant therapy of locally advanced resectable gastric and gastroesophageal junction adenocarcinoma. In addition ，the investigators will explore the relationship between the immunophenotype of gastric cancer and the efficacy and drug resistance of immunotherapy combined with chemotherapy, and screen out biomarkers that can predict the efficacy of immunotherapy.