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OBJECTIVE To investigate the patterns of expression of the junctional proteins β-catenin and claudins in different prognostic groups of patients with prostatic cancer, to determine their value as prognostic markers. PATIENTS AND METHODS We evaluated the samples of 30 patients who had a radical prostatectomy for organ-confined cancer (pT2N0M0), men with clinically advanced cancer, and a control group with benign prostatic hyperplasia. Using immunohistochemistry applied to tissue microarrays, each group was evaluated for claudin-1, -2, -3, -4, -5, -7, -8 and -10, and β-catenin expression. RESULTS There were differences among the three groups in the expression of claudin-1 ( P = 0.001), -2 ( P = 0.014), -3 ( P = 0.027), -4 ( P = 0.001), -8 ( P = 0.001) and β-catenin ( P = 0.002), regardless of Gleason score. By contrast, claudin-5, -7 and -10 patterns were not significantly different among the groups. Furthermore, claudin-1 ( P = 0.014) and -4 ( P = 0.004) could be used to distinguish between those patients who had metastases and those who did not. CONCLUSIONS The pattern of claudin expression could be a novel diagnostic marker in re-classifying adenocarcinomas, and an additional sensitive predictive factor for a clinically poor prognosis. Our results suggest that patients with organ-confined and advanced cancer are subsets with distinct claudin expression profiles, and that claudin-4 is related to cellular differentiation in prostate cancer, which is not only the receptor molecule for the Clostridium perfringens enterotoxin, and thus a theoretical future therapeutic target for prostate cancer, but also a marker of progression. [ABSTRACT FROM AUTHOR]