G/GEJ adenocarcinoma is one of the most common malignant tumors in China, ranking the fifth highest incidence and third highest mortality worldwide. Currently, surgical resection is the preferred treatment for G/GEJ adenocarcinoma, while the 5-year survival rate of patients is lower than 25%. Compared with surgical resection, immunotherapy is proved to be able to effectively prolong the survival time of patients. On one hand, with the continuous promotion of immunotherapy drugs, the exploration of neoadjuvant application of immunotherapy in G/GEJ adenocarcinoma has become a hotspot in recent years. It's also on their way that clinical trials of programmed death receptor-1 (PD-1), programmed death ligand-1 (PD-L1) and other immune checkpoints are carried out. On the other hand, the research found that although the curative effect of immune therapy seems better, the present G/GEJ adenocarcinoma immunotherapy marker researches mainly focused on the late stage of the cancer, with few studies of immune markers of neoadjuvant therapy for G/GEJ adenocarcinoma. Additionally, it's not quite feasible for single biomarkers to predict the immune treatment effect precisely. Therefore, combined with clinicopathology and therapeutic effects, this study is aimed to construct the efficacy prediction model of anti-PD-1 antibody together with chemotherapy for G/GEJ adenocarcinoma, by detecting RNA expression. Furthermore, this study will perform drug sensitivity test and bio-molecular test on patient derived organoid model to validate the biomarkers found from biological specimens.