194 Background: With the introduction of PSA testing, the problem of over-treatment emerged in prostate cancer. Only a small subset of prostate cancer patients will require more intensive adjuvant therapy. There is currently no biomarker that can predict disease aggressiveness at the time of surgery. Methods: We analyzed miRNA expression in 41 patients (the discovery set) which were dichotomized into; 'high risk'- experienced biochemical failure within 24 months after radical prostatectomy (n=26) and 'low risk' who did not have biochemical failure for at least 35 months (n=15). The validation set consisted of 72 cases. Total RNA was isolated from FFPE cores. cDNA was prepared for each patients and expression miRNA expression was screened by qRT-PCR –based panel. miRNAs were ranked by non-parametric tests. Linear regression models were built to predict biochemical failure. We used TargetScan for miRNA target prediction. Targets were validated by transient transfection of synthetic miRNA precursors followed by qRT-PCR quantification of the targets. Proliferation was assessed by measuring cell viability. Results: We compared the expression of 754 mature human miRNAs in patients with ‘high’ or ‘low’ risk for biochemical failure. We identified 24 miRNAs that were differentially expressed between the risk groups. We developed three logistic regression models, based on the expression of 2-3 miRNAs (PPV=100% and NPV ranges 86.4-100%). We confirmed the differential expression on the study set and on a larger, independent set of PCa pateints. We also validated one model on an independent set of patients. Further, we show that transfection of miR-152 and miR-331-3p, featured in the logistic regression models, altered proliferation of PCa3 and DU145 cells. Target prediction indicated Erbb3 and Erbb2 as potential direct targets and their mRNA expression significantly reduced when miR-152 and miR-331-3p were overexpressed. Conclusions: Altered miR-331-3p and miR-152 expression represent a potential tool for assessing the risk of early biochemical failure. These miRNAs may act through the Erbb family to induce an alternative way of AR activation.