Prognostic value of microRNA-9 in cancers: a systematic review and meta-analysis

Recent studies revealed that different microRNA-9 (miR-9) expressions were associated with prognoses of different cancers. We conducted this meta-analysis to evaluate the prognostic value of miR-9. PubMed, Embase, Web of Science, and Cochrane Library (last update by November 30, 2015) were searched for literatures. A total of 17 studies from 16 articles were finally qualified and enrolled in this meta-analysis. Pooled analyses showed that a higher expression of miR-9 might predict poor overall survival (HR: 2.17, 95% CI: 1.39 - 3.41, P < 0.001 (7.23 * 10-4)), disease-free survival (HR: 5.22, 95% CI: 2.17 - 12.53, P < 0.001 (2.21 * 10-4)), and recurrence-free survival (HR: 1.57, 95% CI: 1.32 - 1.85, P < 0.001 (1.80*10-7)) in various carcinomas. However, results of subgroup analyses revealed that down-regulated miR-9 was associated with poor overall survival (HR: 0.45, 95% CI: 0.28 - 0.73, P < 0.001 (1.13*10-3)) and progress-free survival (HR: 0.46, 95% CI: 0.34 - 0.62, P < 0.001 (5.03*10-7)) in ovarian cancer patients. By subgroup analyses we also found that sample collecting time and patients' origin had little influence on the result of OS. These results indicate that in most cancer types the highly expressed miR-9 is associated with poor survival of patients, whereas the down-regulated miR-9 may predict poor prognosis in patients with ovarian cancer.