Abstract. The purpose of the present study was to determine the tissue and plasma levels of microRNA (miR)-155 and miR-31 in 67 patients with invasive intraductal breast cancer and their correlation with the clinicopathological characteristics. Using a quantitative real-time-PCR (qRT-PCR) assay, it was demonstrated that the plasma levels of miR-155 and miR-31 in patients were 6-and 5-fold higher than those in healthy individuals, respectively (P<0.05). In cancerous tissues, miR-155 expression levels were 5-fold higher compared with those in non-cancerous tissues (P<0.05), whereas no difference was observed with miR-31 expression (P>0.05). The expression levels of miR-155, but not miR-31, were inversely correlated with estrogen receptor (ER) and progesterone receptor (PR) expression (ER, r=-0.353, P=0.003; PR, r=-0.357, P=0.003). The tissue and plasma levels of miR-155 and miR-31 were not correlated with epidermal growth factor receptor-2 (HER-2) expression levels. Furthermore, high levels of plasma miR-155 and miR-31 were identified in the tumors of TNM stage II, lymph node metastasis 0-3 and tumor sizes of 2-5 cm in patients who were aged over 52 years. miR-155 was mainly expressed in patients with a pathology score of 3 for ER or PR expression; miR-31 expression was higher in patients with a pathology score of 2. These results suggest that miR-155 and miR-31 are differentially expressed in breast cancer patients. Their correlation with the clinicopathological characteristics may aid the diagnosis and treatment of invasive intraductal breast cancer.

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