The expression of miR-21 and miR-375 predict prognosis of esophageal cancer

Abstract Background MicroRNA is a class of small, well-conserved, non-coding RNAs, and could play a potential role as diagnostic and prognostic biomarkers of esophageal cancers. We aimed to review comprehensively the evidence of microRNA as prognostic biomarkers in esophageal cancers. Methods Studies were identified by searching PubMed, Embase and Web of Science until November 2013. Descriptive characteristics of studies were described and an additional meta-analysis for specific microRNAs which were studied most frequently was performed. Pooled hazard ratios (HRs) and their corresponding 95% confidence intervals (CIs) were calculated. Fixed model or random model method was chosen depending on the heterogeneity among the studies. Results Twenty-two studies including a total of 1946 participants were enrolled after a strict filtering and qualifying process. Among 33 prognostic microRNAs identified for esophageal cancer, miR-21 and miR-375 appeared more frequently. The median study size was 70.5 patients (29–249 patients) and the median HR was 3.305 (IQR = 1.615–7.31). For the studies evaluating miR-21’s association with overall survival (OS), the pooled HR suggested that high level of miR-21 has a negative impact on OS (HR = 1.52[1.17–1.98], P  = 0.001). As for miR-375, the pooled HR for OS (high/low) was 0.53 (95% CI: 0.39–0.73, P