Abstract: Objective To investigate the correlation of the expression of miR-342-3p with the clinicopathological features and long-term prognosis in breast cancer. Methods The breast cancer patients who received the radical mastectomy from January 2014 to February 2015 in Nanping First Hospital were included in the breast cancer group, and the patients with benign breast tumors who received the surgical resection were included in the control group. The expression level of miR-342- 3p in breast cancer tissues and benign breast tumor tissues were detected. The breast cancer patients were followed up until August 2019 to analyze their overall survival (OS) and disease-free survival (DFS). The Kaplan-Meier curve was used to analyze the relationship between the expression level of miR-342-3p and the OS and DFS of the patients. Cox proportional risk model was used to analyze the risk factors affecting the OS and DFS of the patients. The cell viability of MCF7 cells transfected with miR-NC or miR-342-3p mimics were measured. The expression levels of AKT2, Bcl2L1 and FOXQ1 were detected. Results The expression level of miR-342-3p in breast cancer tissues was significantly lower than that in benign breast tumor tissues (P < 0. 05), and statistical difference were found in patients with different T stage, status of lymph node metastasis, molecular typing and Ki-67 expression level (P< 0. 05). The Kaplan-Meier curve analysis showed that the DFS and OS were shorter in patients with lower expression level of miR-342-3p than those in patients with higher expression level of miR-342-3p. COX analysis showed that the status of lymph node metastasis and the expression levels of Ki-67 and mir-342-3p were the risk factors for DFS and OS in breast cancer patients. The expression levels of AKT2, Bcl2L1 and FOXQ1 were lower in breast cancer tissues with highly expressed miR-342-3p than those with lowly expressed miR-342-3p. The cell viability of MCF7 cells overexpressed with miR-342-3p was higher than that in control group. The expression levels of AKT2, Bcl2L1 and FOXQ1 in MCF7 cells overexpressed with miR-342-3p were lower than those in control group. Conclusion miR-342-5p is lowly expressed in breast cancer patients and correlates with the deterioration of their pathological features. Low expression of miR-342-5p is the risk factor for prognosis in breast cancer patients. AKT2, Bcl2L1 and FOXQ1 may be involved in the molecular mechanism of miR-342-5p associated breast cancer progression. 

Key words: breast cancer, miR-342-5p, pathological features, overall survival, disease free survival