Background: Our previous study showed the association of aquaporin 5 (AQP5) up-regulation with cancer proliferation and migration in estrogen receptor (ER)-positive breast cancer cell line (MCF-7) and with unfavorable prognosis in a small number of patients with breast cancer. Accordingly, we analyzed the prognostic impact of AQP5 expression in a large number of patients with early breast cancer (EBC). Methods: AQP5 expression was investigated on the basis of the immunohistochemistry of tissue microarray specimens from 447 EBC patients who underwent surgery between 2003 and 2008. We scored the staining intensity (0 through 3) and percentage of positive tumor cells (0 through 4), and the staining score was defined as sum of these scores used to categorize the AQP5 expression as negative (0 through 2), weak (3 through 5), or strong (6 or more). Results: A total of 267 (59.7 %) patients were identified as AQP5-positive (staining score >2), including 123 (27.5 %) cases of strong expression (stating score >5). In a univariate analysis, AQP5 overexpression was significantly associated with survival for the patients with ER/progesterone receptor (PR)-positive and human epidermal growth factor receptor 2 (HER2)-overexpressed EBC. Moreover, a multivariate survival analysis revealed that AQP5 overexpression was an independent prognostic marker of survival for the EBC patients, which was prominent in patients with ER/PR-positive tumor. However, no difference in AQP5 expression was observed on the basis of patient and tumor characteristics. Conclusions: AQP5 expression in tumor tissue can be considered a prognostic marker in patients with EBC after curative surgery.
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