Introduction: To avoid over-treatment of early stage prostate cancer (PCa), predictive biomarkers for PCa aggressiveness which can be obtained during pre-treatment evaluation are essential. Core 2 beta-1, 6-N-acetylglucosaminyl-transferase-1 (GCNT1) is a key enzyme that forms core 2 branched O-glycans, the expression of which is associated with aggressive potential of prostate cancer. We examined whether GCNT1 expression in prostate biopsy specimen can predict cancer recurrence after radical prostatectomy for the patients with with PCa. We then investigated molecular background for aggressive malignant potential mediated by GCNT1 expression. Methods: Paraffin-embedded PCa biopsy specimens were immunohisto-chemically tested for GCNT1 expression using an anti-GCNT1 monoclonal antibody. We also examined the role of GCNT1 in PCa progression using cell lines which express high or low levels of GCNT1. Results: GCNT1 expression correlated with D' Amico's recurrence risk classification. The GCNT1-positive rate in organ confined PCa was significantly lower than that in PCa with extra-prostatic extension. GCNT1-negative tumors were associated with significantly better prostate-specific antigen (PSA)-free survival compared with GCNT1-positive tumors. Multivariate analysis revealed that GCNT1 expression status was an independent risk factor for PSA recurrence after radical prostatectomy. Subsequent basic study revealed that GCNT1-over-expressing cells produced a significantly larger amount of growth factors when co-cultured with prostate stromal cells compared with GCNT1-knocked down cells and formed larger tumors. Conclusions: GCNT1 expression in prostate biopsy specimen is a significant and independent predictor of recurrence after radical prostatectomy, which can be used in pre-treatment decision making for the patient. Further validation study is necessary to establish clinical implication of GCNT1 in management of PCa. (C) 2016 Elsevier Inc. All rights reserved.