Background: Identification of prognostic markers would be useful in the clinical management of patients with pancreatic ductal adenocarcinoma (PDAC). The clinical relevance of claudin-4 (CLDN4), recently identified as overexpressed in PDAC, is unknown. Methods: Using quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR), we analyzed CLDN4 mRNA expression in a panel of 9 pancreatic cancer cell lines and formalin-fixed paraffin-embedded (FFPE) tissues from 100 patients with PDAC. The CLDN4 expression levels were then correlated with clinicopathological variables and patient outcome. We also performed immunohistochemical analysis in 20 FFPE samples of PDAC to investigate the expression of CLDN4 protein. Results: Increased expression of CLDN4 was confirmed in all the pancreatic cancer cell lines tested compared with normal ductal epithelial cells and fibroblasts. We found that low expression of CLDN4 was significantly associated with shorter survival in patients with PDAC (hazard ratio; 1.362, 95% confidence interval; 1.011-1.873, P = 0.0419). Patients with high CLDN4 expression survived longer for a median of 63.0 months, compared with 14.7 months in patients with low CLDN4 expression (P = 0.0067). In immunohistochemical analysis, the level of CLDN4 mRNA expression was significantly correlated with the expression of CLDN4 protein (P = 0.0168). Conclusion: Increased expression of CLDN4 mRNA predicts better prognosis in PDAC.
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