This study assessed their causal role in STAD, prognostic value, and developed a histopathology-based model to predict MutS homolog 2 (MSH2) expression.<h4>Methods</h4>Using data from the IEU OpenGWAS database, five Mendelian randomization (MR) models evaluated causal links between MMR genes and gastric cancer (GC). Here, MSH2 is linked to gastric cancer.