Low-frequency microsatellite instability in genomic di-nucleotide sequences correlates with lymphatic invasion and poor prognosis in gastric cancer.

The clinical significance of low-frequency microsatellite instability (MSI-L) in gastric cancer (GC) has not been well established. The aim of this study was to evaluate the clinicopathological features of MSI-L in GC. We investigated microsatellite instability (MSI) in 5 di-nucleotide repeat sequences in 210 unselected GC patients. High-resolution fluorescent microsatellite analysis assay was utilized to detect MSI. Clinicopathological variables were compared among groups with different microsatellite statuses. The overall survival (OS) was analyzed by Kaplan-Meier method. Multivariable analysis was performed to identify prognostic factors and variables correlated with lymph node metastasis. High-frequency microsatellite instability (MSI-H), MSI-L, and microsatellite stable were identified, respectively, in 10.5, 10.0, and 79.5% of unselected GC cases. Tumors with MSI-H were less invasive, and these patients showed a better OS. MSI-L was correlated with more advanced tumor Node Metastasis stage, and more frequent lymph node metastasis. The unfavorable prognosis predicted by MSI-L was ascribed to its correlation with lymphatic invasion. MSI-L characterized by di-nucleotide markers represents a distinct subcategory of GC with aggressive clinicopathological features, which are particularly affiliated to lymphatic system and correlated with a poor prognosis. MSI-L could be beneficial for predicting the clinical outcome of GC.