Down-Regulated microRNA-421 Was Associated with the Poor Prognosis of Breast Cancer Patients

Background: Breast cancer is one of the most common cancers among females with high morbidity and mortality. MicroRNAs (miRNAs) have been reported to play important roles in the development of cancers. However, the prognostic value of microRNA-421 (miR-421) in breast cancer have not been extensively explored.Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the relative expression of miR-421 in breast cancer tissue samples. Relationships between miR-421 expression and clinicopathological factors were analyzed by chi-square test. The effects of several variables on survival status were tested by Kaplan-Meier curve and Cox proportional hazards regression analyses.Results: MiR-421 expression was significantly decreased in breast cancer tissues, compared with adjacent noncancerous tissues (P<0.001). Moreover, abnormal miR-421 expression was closely correlated with lymph node metastasis (P<0.001), TNM stage (P=0.021), and differentiation (P=0.044) of breast cancer patients. Kaplan-Meier analysis revealed that patients with low miR-421 expression had a shorter overall survival time than those with high miR-421 expression (P=0.001). Furthermore, multivariate analysis demonstrated that miR-421 (P=0.014, HR=2.000, 95%CI: 1.149-3.480) was an independent prognostic indicator in breast cancer patients, as well as lymph node metastasis (P=0.016, HR=1.987, 95%CI: 1.137-3.474).Conclusion: The reduced expression of miR-421 may predict the poor prognosis of breast cancer and miR-421 may be involved in the progression of breast cancer.