Microsatellite instability is associated with a better prognosis for gastric cancer patients after curative surgery

Background Microsatellite instability (MSI) is one of the leading mechanisms for the carcinogenesis of gastric cancer. Its prognostic value is controversial. Methods Between May 1988 and Oct 2003, a total of 214 gastric cancer patients undergoing curative surgery were enrolled, and their MSI statuses were classified as MSI-H (high) or MSI-L/S (low/stable). The clinicopathologic characteristics of MSI-H and MSI-L/S gastric cancers were compared. Results The MSI-Htumors accounted for 11.7 %(n = 25) of the 214 total gastric cancers. Although not statistically significant, the MSI-H gastric cancers were more frequently located in the lower third of the stomach (64 % vs. 49.2 %) and were more often the intestinal type (72 % vs. 61.4 %) compared to the MSI-L/S gastric cancers. The MSI-Hgastric cancers had a significantly better 5-year overall survival (OS) rate (68 % vs. 47.6 %, p = 0.030) and a trend of a better 3-year disease-free survival rate (71.8 % vs. 55.2 %, p = 0.076) compared to the MSI-L/S gastric cancers. A multivariate analysis revealed that pathologic TNM stage and MSI status were the independent prognostic factors for OS after curative surgery. Conclusions Compared to MSI-L/S tumors, MSI-H tumors are associated with a better OS rate for gastric cancer patients after R0 resection.