In this study, for the first time, we revealed that the tumor cell-intrinsic cGAS–STING is highly expressed in dMMR GC compared to pMMR/EBV (−) GC, and the high expression of tumor cell-intrinsic STING is significantly associated with the high infiltration of CD8+ T cells in dMMR GC in our own cohort. Here, CD8A is linked to neoplasm.