Emerging evidence has shown that aberrant microRNA expression has the potential to be used for predicting survival and treatment response of malignant neoplasms. In recent years, the role of miR-9 had been investigated in various types of cancers, and it was found that the results were inconsistent and inconclusive. Hence, in this study, a meta-analysis was conducted to assess the prognostic value of miR-9 in various types of tumors. Eligible studies were identified through a systematic search in PubMed and EMBASE and then were assessed by further quality evaluation. Pooled hazard ratios (HRs) with 95% confidence intervals for overall survival (OS) were calculated to investigate the association between miR-9 expression and cancer prognosis. The pooled results of eight published studies showed that elevated miR-9 was a predictor of poor survival of various carcinomas, with pooled HR of 3.04 (95% confidence interval: 1.96-4.73) for OS. Subgroup analysis on the basis of tumor type, sample size, and HR estimate also showed that high levels of miR-9 were also significantly correlated with OS. In addition, when the subgroup analyses were grouped by follow-up time, it was found that the elevated expression of miR-9 was associated with a lower long-term survival when the follow-up time was >60 months, but there was no correlation between the outcomes and those patients whose follow-up time was <60 months. Funnel plots and Egger's tests revealed that there was no obvious publication bias risk in the meta-analysis. In conclusion, our results demonstrated that higher expression level of miR-9 significantly predicted worse OS in various carcinomas and that miR-9 may act as a novel biomarker in the prognosis of malignant neoplasms.
Keywords: malignant neoplasms; meta-analysis; microRNA-9; overall survival; prognosis.