High expression levels of miR-21 and miR-210 predict unfavorable survival in breast cancer: a systemic review and meta-analysis.

Background: MicroRNAs (miRNAs) have been emerging as valuable prognostic biomarkers of breast cancer. We therefore summarized recent research into miRNAs involved in human breast cancer and, further, completed a meta-analysis to predict the role of specific miRNAs in the survival of breast cancer patients.
Methods: Studies were identified by searching PubMed, Embase and Web of Science. Descriptive characteristics for studies were described, and an additional meta-analysis for specific miRNAs was performed. Pooled hazard ratios (HRs) and their corresponding 95% confidence intervals (CIs) were calculated.
Results: A total of 41 articles including 27 types of miRNAs were found regarding prognostic biomarkers for breast cancer survival, of which, micRNA-21 (miR-21) was the most-studied specific miRNA that appeared repeatedly among the selected classifiers. For the studies evaluating miR-21's association with clinical outcomes, the median HR in the studies was 2.32 (interquartile range [IQR] = 1.04-3.40), and the pooled HR suggested that high expression of miR-21 has a negative impact on overall survival (OS; HR = 1.46, 95% CI, 1.25-1.70; p<0.05) and disease/recurrence-free survival in breast cancer (HR = 1.49, 95% CI, 1.17-1.90; p<0.01). We also found that higher expression levels of miR-210 significantly predicted poorer outcome, with median HR in the reported studies of 4.07 (IQR = 1.54-4.43) and a pooled HR of 2.94 (95% CI, 2.08-4.17; p<0.05).
Conclusions: These results indicate that miRNAs show promising associations with prognosis in breast cancer. Moreover, specific miRNAs such as miR-21 and miR-210 can predict poor survival rates in breast cancer patients.