High microsatellite instability predicts good prognosis in intestinal-type gastric cancers

Background and Aim: A subset of gastric cancers showed high microsatellite instability (MSI-H). The reported clinicopathological features of MSI-H gastric cancers are heterogeneous, and specific factors associated with prognosis have not been identified. Methods: We analyzed the clinicopathological characteristics and prognostic factors in a large series (161 cases) of MSI-H gastric cancers, and compared the results to 315 cases of microsatellite-stable or low microsatellite-instable gastric cancers. Results: The frequency of MSI-H gastric cancers was 9% (161/1786). MSI-H gastric cancers have distinct clinicopathological features, including female sex, older age, antral location, well-to-moderate differentiation, intestinal-type Lauren classification, expanding-type Ming classification, a non-signet-ring cell component, the presence of a mucinous component, a moderate-to-severe lymphoid stromal reaction, and a lower tumor stage. The MSI-H phenotype was associated with better prognosis (P = 0.044), and male sex (P = 0.035, hazard ratios [HR]: 0.23), intestinal-/mixed-type Lauren classification (P < 0.001, HR: 0.09) and lower tumor stages (1 and 2, P = 0.001, HR: 0.08) were independently-favorable prognostic factors. Conclusions: With unique clinicopathological features, intestinal-type MSI-H gastric cancers are associated with good prognosis and can be classified as a different subset of gastric cancers.