miR-320a is an independent prognostic biomarker for invasive breast cancer

Breast cancer is one of the most common malignancies worldwide and is the second leading cause of cancer-related mortality among females. miRNAs are a class of small noncoding RNAs that are aberrantly expressed in human cancers. Due to their small size and stability, miRNAs have the potential to be efficacious clinical targets. MicroRNA-320a (miR-320a) has been shown to be dysregulated in multiple malignancies. In the present study, the expression levels of miR-320a were investigated in 15 paraffin-embedded in situ breast carcinoma and 130 invasive breast cancer tissues, and the prognostic value for breast cancer patients was assessed. Chromogenic in situ hybridization revealed that 60/130 (46%) invasive breast cancer tissues exhibited high expression levels of miR-320a (staining index score of ≥4). Furthermore, miR-320a staining was found to significantly correlate with tumor size (P=0.046), clinical stage (P<0.001), lymph node metastasis (P<0.001) and distant metastasis (P=0.006). In addition, patients exhibiting low miR-320a expression levels had shorter overall survival times (P<0.001). Univariate and multivariate analyses revealed that miR-320a was an independent prognostic biomarker for invasive breast cancer (hazard ratio, 0.221; 95% confidence interval, 0.050-0.979; P=0.047). Receiver operator characteristic curves revealed that the prognostic value of miR-320a was enhanced when compared with the widely used prognostic biomarkers (estrogen receptor, progesterone receptor and human epidermal growth factor-2) in invasive breast cancer. The results of the present study suggest that miR-320a presents a potential biomarker for the prognosis of invasive breast cancer, and dysregulation of miR-320a may be involved in invasive breast cancer progression.