High expression of miR-21 and miR-155 predicts recurrence and unfavourable survival in non-small cell lung cancer.

We synthesised the evidence of microRNAs as prognostic biomarkers in lung cancer. Studies were identified by searching PubMed, Embase and Web of Science until March 2012. Descriptive characteristics for studies were described and an additional meta-analysis for two specific microRNAs (miR-21 and miR-155) which were studied extensively was performed. Pooled hazard ratios (HRs) and their corresponding 95% confidence intervals (CIs) were calculated. The median study size was 88 patients (interquartile range [IQR]=53-193) and the median HR in the studies that reported statistically significant results was 2.855 (IQR=2.01-5.035). For the studies evaluating miR-21's association with clinical outcomes, the pooled HR suggested that high expression of miR-21 has a negative impact on overall survival (OS) in non-small cell lung cancer (NSCLC) (HR=2.32[1.17-4.62], P<0.05) and recurrence-free survival (RFS)/cancer-specific survival (CSS) in lung adenocarcinoma (HR=2.43[1.67-3.54], P<0.001). As for miR-155, the pooled HR for OS was 2.09 (95%CI: 0.68-6.41, P>0.05) which was not statistically significant, but for RFS/CSS was 1.42 (95% CI: 1.10-1.83, P=0.007). These results indicate that microRNAs show promising associations with prognosis in lung cancer; moreover, specific microRNAs such as miR-21 and miR-155 can predict recurrence and poor survival in NSCLC.