Abstract. In the context of gastric cancer, microsatellite instability (MSI) is associated with distinct clinicopathological features, including the intestinal histological type, the presence of tumor-infiltrating lymphocytes, and a generally more favorable disease course. This review summarizes current knowledge on the molecular basis of MSI, methods for its detection (immunohistochemistry, PCR using microsatellite marker panels, and next-generation sequencing), and discusses its prognostic and predictive value. According to large clinical studies and meta-analyses, MSI can serve as an independent favorable prognostic factor in patients with resectable GC and as a potential biomarker for responsiveness to immunotherapy. Additionally, MSI status may indicate reduced effectiveness of adjuvant chemotherapy, underscoring the importance of patient stratification and the implementation of personalized treatment strategies.
Keywords: gastric cancer, microsatellite instability, MMR deficiency, molecular classification, immunohistochemistry, immunotherapy, personalized treatment