Prognostic Implications of MicroRNA-21 Overexpression in Invasive Ductal Carcinomas of the Breast

PURPOSE: Among more than 500 microRNAs, microRNA-21 (miR-21) is known to act as an oncogene. The aim of this study was to investigate the significance of miR-21 expression level in relation with clinicopathological factors and prognosis in breast cancer. METHODS: MicroRNA was extracted from cancer and normal breast tissue of 109 breast cancer patients who underwent surgery from 2002 to 2004 using the Taqman® MicroRNA Assay. The correlation between miR-21 expression and clinicopathologic features was analyzed and the significance of miR-21 as a prognostic factor and its relationship with survival was determined. RESULTS: MiR-21 expression was higher in cancer tissues than in normal tissues (p<0.0001). High miR-21 expression was associated with mastectomy, larger tumor size, higher stage, higher grade, estrogen receptor (ER) negative, human epidermal growth factor receptor 2 (HER2) positive, HER2 positive breast cancer subtype, high Ki-67 expression, and death. On multivariate analysis, prognostic factors for overall survival were ER and miR-21. High miR-21 expression was significantly related to lower overall survival (p=0.031). CONCLUSION: This study supports the role of miR-21 as an oncogene and a biomarker for breast cancer with its high expression in cancer tissues and its relationship with other prognostic factors and survival.