Background and Objective The relationship between survival in gastric cancer patients and the status of microsatellite instability (MSI) has not yet been established. The purpose of this meta-analysis was to obtain integrated and more precise data for the value of MSI as a prognostic marker in gastric cancer. Methods A comprehensive systematic review and meta-analysis were conducted using major electronic databases (PubMed, EMBASE, and the Cochrane Central) with keywords related to "microsatellite instability," "gastric cancer," and "prognosis." Results Twenty-four studies with 5,438 participants (712 cases were MSI gastric cancer) were included for pooling risk estimates of MSI in gastric cancer. Seventeen studies reported overall survival. The pooled hazard ratio (HR) for overall survival of MSI vs. non-MSI was 0.72 (95%CI: 0.59-0.88, P = .001) in a random-effects model. In the sensitivity analysis, the result from the most recent study showed the most heterogeneity. Conclusion MSI gastric cancer was associated with good prognosis but there was heterogeneity in the recent studies. Changed epidemiology and effects of chemotherapy are potential causes of heterogeneity. Establishing a consensus for defining MSI in gastric cancer should be preferred for future studies.
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