Purpose: To establish xenograft mouse models of metastatic and nonmetastatic human prostate cancer and to apply these models to the search for aberrant glycosylation patterns associated with tumor progression in vivo and in patients.Experimental Design: Prostate cancer cells (LNCaP, PC-3, LuCaP 23.1, and DU-145) were xenografted subcutaneously into immunodeficient pfpÀ/À mice. Tumor growth and metastasis formation were quantified and as altered glycosylation patterns have been associated with metastasis formation in several other malignancies, prostate cancer cells were profiled by a quantitative real-time PCR (qRT-PCR) glycosylation array and compared with normal human prostate cells. The activity of upregulated glycosyltransferases was analyzed by their sugar residues end products using lectin histochemistry on primary tumors and metastases in the animal experiments and on 2,085 clinical samples.Results: PC-3 cells produced the largest number of spontaneous lung metastases, followed by LNCaP and LuCaP 23.1, whereas DU-145 was nonmetastatic. qRT-PCR revealed an upregulation of b1,6-Nacetylglucosaminyltransferase-5b (Mgat5b) in all prostate cancer cell lines. Mgat5b products [b(1,6)-branched oligosaccharides] were predominantly detectable in metastatic xenografts as shown by increased binding of Phaseolus vulgaris leukoagglutinin (PHA-L). The percentage of prostate cancer patients who were PHA-L positive was 86.5. PHA-L intensity correlated with serum prostate-specific antigen and a cytoplasmic staining negatively affected disease-free survival.Conclusion: We show a novel xenograft mouse model for human prostate cancer respecting the complete metastatic cascade. Specific glycosylation patterns reveal Mgat5b products as relevant markers of both metastatic competence in mice and disease-free survival in patients. This is the first description of Mgat5b in prostate cancer indicating a significant biologic importance of b(1,6)-branched oligosaccharides for prostate cancer progression.