In a variety of solid tumors such as colorectal cancer, it has been confirmed that some selected advanced patients still have a chance to cure through multidisciplinary treatment. Because of the poor biological behavior of gastric cancer, few people with advanced gastric cancer can benefit from local treatment, and there are fewer related studies. However, retrospective and small sample size prospective phase II clinical studies have also shown that unresectable locally advanced and some selected limited distant metastatic gastric and gastric junction adenocarcinoma patients may also achieve long-term survival through multimodal treatment strategies. The triple drug regimens were often used as conversion regimens in previous studies. Although the efficiency was improved, the R0 resection rate was only about 60%, the disease-free survival was about 10 months, and the toxicity was high. In order to improve the survival of these patients, more effective and less toxic treatment regimens are urgently needed. Objective response rate was 76.5% with anti-PD-1 antibody nivolumab plus CapeOX. The investigators predict that this regimen will achieve good results in the conversion treatment of advanced gastric cancer. The investigators intend to carry out this study to evaluate the efficacy and safety of Sintilimab plus CAPOX in the conversion therapy for patients with unresectable locally advanced or limited metastatic adenocarcinoma of the stomach or esophagogastric junction. The primary objectives are 12-month progression- free survival (PFS) rate. Secondary objectives include safety, objective response rate (ORR), R0 resection rate , tumor regression grading（TRG）, progression- free survival (PFS) ，overall survival (OS) and exploratory biomarker assessment. Subjects enrolled are treated with oral capecitabine 1000mg per m2 bid for two weeks（every 3 weeks）and intravenous oxaliplatin 130mg per m2（every 3 weeks）in combination with sintilimab 200mg (every 3 weeks) for 3 cycles. After 3 cycles of treatment, the tumor was evaluated. The clinical efficacy was evaluated as CR\PR\SD. Patients with SD,PR,CR will be treated with surgery. 36 patients will be included in this study
This study aims to evaluate the efficacy and safety of Sintilimab plus CAPOX in the conversion therapy for patients with unresectable locally advanced or limited metastatic adenocarcinoma of the stomach or esophagogastric junction