Microsatellite instability and survival in gastric cancer: A systematic review and meta-analysis.

Microsatellite instability (MSI) is associated with the prognosis in several cancers and is used for determination of the chemotherapy regimen in stage II colon cancer in the National Comprehensive Cancer Network guideline. However, the association between MSI and the prognosis of gastric cancer remains unclear. PubMed database was searched until January 2014 using MeSH terms and key words to identify the studies evaluating MSI and prognosis of gastric cancer and the references were manually searched. The main outcome was the overall survival rate and the subordinate outcome was the association between high-frequency MSI (MSI-H) and clinicopathological characteristics. Eight studies met the inclusion criteria and the majority of data were collected retrospectively. There were 1,976 patients, 431 of which were MSI-H patients, with a range of 11.68-33.82%. Four studies used the National Cancer Institute panel to define MSI-H, the other four had microsatellite markers ranging 2-11. Significant associations were found in three studies and the overall summary estimate was hazard ratio, 0.63 (95% confidence interval, 0.52-0.77), with no evidence of inter-study heterogeneity (I2=0.0%). MSI-H patients were identified to have a tendency to have less lymph node (LN) metastasis, superficial tumor invasion and to be intestinal type. In conclusion, MSI-H gastric cancers have an improved prognosis, accompanied with reduced risk of LN metastasis, tumor invasion and mortality.