Selecting Patients Who May Benefit From Immunotherapy by Tissue-based Biomarkers.

Collect tumor tissue of 300 gastric cancer patients at treatment baseline, samples will be transferred to central lab to detect the density and spatial proximity of certain immune cells infiltrated in tumor by multi complex immunohistochemistry, and evaluate patients' TIIC signature.Tumor response evaluation will be performed after two cycles of therapy by CT/MRI based on RECIST.Clinical data, including tumor stage,metastaticorgan ,regimen, objective response, progression free survival, overall survival, etc, will be collected according to study protocol.