Association between primary tumor site, perioperative CEA ratio, and overall survival in patients with colorectal cancer.

Abstract

518 Background: There are differences in the incidence, clinical presentation, molecular pathogenesis and outcome of colorectal cancer (CRC) based on the tumor location. Emerging research suggests that the perioperative carcinoembryonic antigen (CEA) ratio is a prognostic factor for CRC patients. We aimed to determine the association between tumor location, perioperative CEA ratio, and 5-year survival among patients with CRC. Methods: We analyzed 111 patients who underwent resection for CRC at KUMC. After excluding patients without pre- or post-operative CEA data, 62 patients for whom we could calculate a CEA ratio (post-op/pre-op CEA) were classified as either high ( ≥ 0.5) or low ( < 0.5) ratio. The primary outcomes were: 1) overall survival (OS) stratified by tumor location; 2) OS stratified by CEA ratio; and 3) whether there was effect modification by tumor location, of the association between perioperative CEA ratio and OS, after adjusting for tumor stage and smoking status. Kaplan-Meier method was used to estimate survival rates, and Cox proportional hazards models for multivariate analysis. Results: The median age was 61 years, 54% male, 31% smokers, 74% left-sided tumors, median pre-operative CEA was 3.3, and 60% had CEA ratio ≥ 0.5. The OS rates were 89.1% and 81.3% in patients with left-sided versus right-sided tumors respectively (p-value = 0.4). The OS rates were 83.8% and 92.0% in patients with high versus low CEA ratios respectively (p-value = 0.3). There was effect modification by tumor location on association between CEA ratio and OS, after adjusting for smoking status and tumor stage (p-value < 0.001). However, in the stratified analysis, the n was too small to permit inferential analysis. In multivariate analysis, both tumor location (HR 0.4; p = 0.3) and perioperative CEA ratio (HR 2.7; p = 0.3) were not significantly associated with OS after adjusting for smoking status and tumor stage. Conclusions: There was no difference in OS between left versus right-sided tumors. The association between perioperative CEA ratio and OS was significantly modified by tumor location. However, to attribute this modification to left versus right warrants validation in a larger cohort as our sample size was limited.