Decreased Tumoral Expression of Colon-Specific Water Channel Aquaporin 8 Is Associated with Reduced Overall Survival in Colon Adenocarcinoma

BACKGROUND: Colon cancer survival is dependent on metastatic potential and treatment. Large RNA-sequencing data sets may assist in identifying colon cancer-specific biomarkers to improve patient outcomes. OBJECTIVE: This study aimed to identify a highly specific biomarker for overall survival in colon adenocarcinoma by using an RNA-sequencing data set. DESIGN: Raw RNA-sequencing and clinical data for patients with colon adenocarcinoma (n = 271) were downloaded from The Cancer Genome Atlas. A binomial regression model was used to calculate differential RNA expression between paired colon cancer and normal epithelium samples (n = 40). Highly differentially expressed RNAs were examined. SETTINGS: This study was conducted at the University of Louisville using data acquired by The Cancer Genome Atlas. PATIENTS: Patients from US accredited cancer centers between 1998 and 2013 were analyzed. MAIN OUTCOME MEASURES: The primary outcome measures were recurrence-free and overall survival. RESULTS: The median age was 66 years (147/271 men, 180/271 White patients). Thirty RNAs were differentially expressed in colon adenocarcinoma compared with paired normal epithelium, using a log-fold change cutoff of ±6. Using median expression as a cutoff, 4 RNAs were associated with worse overall survival: decreased ZG16 (log-rank = 0.023), aquaporin 8 (log-rank = 0.023), and SLC26A3 (log-rank = 0.098), and increased COL1A1 (log-rank = 0.105). On multivariable analysis, low aquaporin 8 expression (HR, 1.748; 95% CI, 1.016-3.008; p = 0.044) was a risk factor for worse overall survival. Our final aquaporin 8 model had an area under the curve of 0.85 for overall survival. On subgroup analysis, low aquaporin 8 was associated with worse overall survival in patients with high microsatellite instability and in patients with stage II disease. Low aquaporin 8 expression was associated with KRAS and BRAF mutations. Aquaporin 8 immunohistochemistry was optimized for clinical application. LIMITATIONS: This was a retrospective study. CONCLUSION: Aquaporin 8 is a water channel selectively expressed in normal colon tissue. Low aquaporin 8 expression is a risk factor for worse overall survival in patients who have colon cancer. Aquaporin 8 measurement may have a role as a colon-specific prognostic biomarker and help in patient risk stratification for increased surveillance. See Video Abstract at http://links.lww.com/DCR/B603.