High MicroRNA-370 Expression Correlates with Tumor Progression and Poor Prognosis in Breast Cancer

Purpose: Deregulation of microRNA-370 (miR-370) has been reported in various cancers, in which it can act as either an oncogene or a tumor suppressor gene. However, the clinicopathologic significance of miR-370 expression in breast cancer has not been studied. Methods: The expression of miR-370 was determined with quantitative real-time polymerase chain reaction in 60 formalin-fixed, paraffin-embedded primary breast cancer tissues. Additionally, the protein expression levels of previously known targets of miR-370, such as FOXM1, FOXO1, and FOXO3a, were detected using immunohistochemistry. Finally, we analyzed its correlation with target protein expression, clinicopathologic features, and clinical outcome. Results: High levels of miR-370 expression correlated with lymph node metastasis (p=0.009), advanced stage (p=0.002), and frequent perineural invasion (p=0.042). Moreover, patients with high miR-370 expression had poor disease-free survival compared with the low-expression group. However, no correlation was observed between miR-370 and its target protein expression. Conclusion: Our results indicate that upregulation of miR-370 in breast cancer is correlated with breast cancer progression and that it might be a potential biomarker for predicting clinical outcomes.