OBJECTIVETo investigate the potential use of miR-155 as novel breast cancer biomarker.

METHODSThere were 88 breast cancer patients underwent modified mastectomy and had detailed clinical follow-up information. Extracting RNA from the formalin-fixed paraffin embedded (FFPE) samples, miR-155 levels were quantified by real-time-PCR. miR-155 levels among clinico-pathological variables were accessed by Mann Whitney-U test. Overall survival curve was derived from Kaplan-Meier estimates and the curve was compared by Log-rank test. Cox regression analysis was used for multivariate analysis. All statistical tests were two-sided.

RESULTSSignificantly higher miR-155 level was found in tumor tissue compared to paired normal tissue (t = 6.75, P = 0.000). A potential relationship between miR-155 levels and existing clinico-pathological parameters of breast cancer, such as menstrual status, tumor size, nodal involvement, stage of disease, hormone receptor status, HER-2 status, histological grade or tumor subtype was investigated. Up-regulated miR-155 level was observed in breast cancer with lymph node metastasis, pT3+4, advanced TNM stage, HER-2 positive and with vascular invasion (Z = -6.320 to -2.041, P = 0.000 to 0.041). When considering 2(-ΔCt) = 4.87 (median level) as cut-off value, patients with miR-155 up-regulation showed a positive association towards a shorter overall survival (χ(2) = 6.396, P = 0.011). In Cox multivariate analysis, miR-155 expression on FFPE was shown an inverse trend for outcomes of breast cancer (HR = 1.58, 95%CI: 0.87 - 3.16, P = 0.082).

CONCLUSIONSmiR-155, as an oncomir, promotes lymph node involvement and vascular invasion and accompanies over-expressed HER-2 on breast cancer FFPE tissue. It suggests that miR-155 could predict the invasiveness.