MicroRNA-21 as an Indicator of Aggressive Phenotype in Breast Cancer

Objective: The recently discovered microRNAs (miRNAs) are non-protein-coding, endogenous small RNAs. The aim of this study was to investigate the relationship between microRNA-21 (miR-21) and the clinicopathological features of breast cancer. Materials and Methods: Formalin-fixed, paraffin-embedded (FFPE) tissue samples were collected from 15 patients who had undergone surgery for primary breast cancer. The miR-21 expression levels in normal and cancer tissues were analyzed using real-time quantitative reverse transcriptase polymerase chain reaction (real-time qRT-PCR). The correlations between the miR-21 expression level and the stage of disease, the tumor size, lymph node involvement, hormone receptor status, human epidermal growth factor receptor 2 (HER2) status, and disease-free survival (DFS) were investigated. Results: The miR-21 expression levels were significantly higher in patients with stage Ill disease, patients with more than 3 axillary lymph node metastases and HER2-positive patients than in patients with stage I-II disease, patients with 1-3 axillary lymph node metastases and HER2-negative patients (p = 0.005, p = 0.037, and p = 0.014, respectively). Patients with high miR-21 expression level had a significantly shorter DFS than patients with low miR-21 expression level (median DFS: 18 and 56 months, respectively; p = 0.004). Conclusion: These results show that miR-21 is an indicator of an aggressive breast cancer phenotype and that it may be a new therapeutic target in the treatment of breast cancer in the future.