miR-155 and miR-31 are differentially expressed in breast cancer patients and are correlated with the estrogen receptor and progesterone receptor status.

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.