Prognostic value of circulating microRNA-21 for breast cancer: a systematic review and meta-analysis

Background: There is an urgent need for novel noninvasive prognostic molecular tumor marker for monitoring the recurrence of breast cancer. MicroRNA-21 (miR-21) play a crucial role in the progression and aggressiveness of breast cancer, but its prognostic significance for patients with breast cancer remains inconclusive. The aim of this meta-analysis is to summarize the role of circulating miR-21 as a molecular marker in patients with breast cancer. Material and methods: Eligible studies were searched from the PubMed, EMBASE and Web of Science databases. The (2) and I-2 tests were used to evaluate heterogeneity between studies. The pooled hazard ratios (HR) with 95% confidence interval (CI) were calculated by a fixed-effects model, if no heterogeneity existed. If there was heterogeneity, a random-effects model was applied. The meta-analysis was conducted using the Review Manager 5 software. Results: A total of 7 articles which included 1629 cases were selected for the meta-analysis. Elevated miR-21 expression was significantly predictive of poor overall survival (HR = 1.51, 95%CI 1.15-1.98, p=0.003). The subgroup analysis consisted of in tissue sample (HR = 1.66, 95%CI 1.03-2.67, p=0.04) and serum sample (HR = 1.73, 95%CI 1.22-2.46, p=0.002). The association between miR-21 expression level and lymph node metastasis was statistically significant (OR = 2.36, 95%CI 1.04-4.78, p=0.03). Conclusion: Our findings suggest that the circulating miR-21 expression level can predict poor prognosis in patients with breast cancer.