PO-499 Comparison of expression of miR21’s guide strand (5P) and passenger strand (3P) in breast tumour progression

Introduction miR-21 is an oncomir that is overexpressed in many types of solid tumours. According to some studies miR-21 expression is higher in breast tumours than normal breast tissue and it is significantly correlated with shorter survival of patients. Many studies have focused on miR-21–5 p and its correlation with clinic pathological features and survival of breast tumours. In some of the studies miR-21–5 p expression has been shown to be associated with ER status, PR status, HER2 status, clinical stage, lymph node, tumour grade and size. The purpose of this study was to compare the expression of miR-21–3 p and miR-21–5 p in progression of breast tumours and their association with corresponding clinic pathological data from the breast cancer patients. Material and methods Six non-neoplastic breast tissues and 144 tumours, from breast cancer patients diagnosed 1987–2003, were obtained from the Department of Pathology at Landspitali University Hospital. The expression levels of miR-21–3 p and miR-21–5 p were measured with StepOnePlus Real-Time PCR System by applying EXIQON primer sets and SYBR Green master mix using miR-16–5 p as endogenous control. Results and discussions miR-21–5 p was expressed at significantly higher levels than miR-21–3 p in both normal (p=0.0003) and tumour tissues (p=6.378e-12). A significant difference was not observed between miR-21–5 p expression in normal breast tissue and tumours. High miR-21–5 p expression correlated significantly with HER2 expression (p=0.001) but it did not correlate with other clinical and pathological factors or survival. miR-21–3 p was expressed at significantly higher levels in tumour tissues than normal breast tissue (p=0.003). Its expression was significantly higher in tumours from patients with metastasis than without metastasis (p=0.02). Furthermore, higher levels of miR-21–3 p correlated with shorter disease free survival (p=0.03, HR=1.72, 95%CI=1.03–2.9). Conclusion Although miR-21 is one of the most studied and upregulated miRNAs in human solid tumours the comparison of miR-21–3 p expression with miR-21–5 p expression in breast tumours has not been well studied. Our results suggest that miR-21–3 p could be a better indicator of breast cancer progression than miR-21–5 p. More studies in larger breast cohorts and functional cell based assays will be needed to shed light on the potential role of miR-21–3 p in breast tumours progression.