Background: Aquaporin 1 (AQP1) is a water channel expressed in many epithelial tissues and endothelium, including the proximal nephron of the kidney.
Objective: We measured AQP1 expression in primary renal cell carcinomas (RCCs) and evaluated its significance and prognostic utility.
Design, setting, and participants: We examined AQP1 expression in 559 sporadic renal tumors as well as in 43 normal kidney tissue samples and collected clinicopathologic and prognostic data.
Measurements: AQP1 expression was measured by using real-time quantitative polymerase chain reaction (PCR).
Results and limitations: All normal kidney samples presented substantial AQP1 expression. Among tumor subtypes, AQP1 expression was significantly higher in clear-cell and papillary RCCs, whereas it was lower in chromophobe RCCs, oncocytomas, and collecting-duct carcinomas. In clear-cell RCC, AQP1 was significantly higher in patients without symptomatic presentation or whose tumors were smaller, lower grade, or either lower stage or lacking in microvascular invasion. Von Hippel-Lindau (VHL) tumor suppressor gene mutational status did not affect expression level. Cox univariate and multivariate analyses strongly associated high AQP1 expression with better prognosis in cancer-specific and cancer-free survival tests in all patient cohorts, as well as in cancer-specific survival in a cohort of patients with advanced metastatic RCC. The time-dependent receiver operation characteristic (ROC) analyses, combined with logistic regression models, revealed that the addition of the AQP1 parameter to the University of California Los Angeles Integrated Staging System (UISS) prognostic score can improve the accuracy of predictions of both cancer death and recurrence for all patient cohorts as well as of cancer death for advanced cases within a 5-yr follow-up period in clear-cell RCC. High AQP1 expression was also associated with better outcome in a univariate cancer-specific survival test in papillary RCCs.
Conclusions: AQP1 shows RCC subtype-specific expression, and its expression level provides useful prognostic information for patients with clear-cell RCC.