Prognostic Value of the Microsatellite Instability Status in Patients With Stage II/III Rectal Cancer Following Upfront Surgery

Abstract

BackgroundWe investigated whether the microsatellite instability (MSI) status affects the survival outcomes in patients with stage II/III rectal cancer who have undergone an upfront curative resection. Patients and MethodsA total of 1103 patients with curatively resected stage II/III rectal cancer who had available polymerase chain reaction-based MSI results were included in the final analysis. ResultsTwenty-four (2.2%) patients in the total cohort were found to be MSI-high (MSI-H). In univariate analysis, neither disease-free survival (DFS) nor overall survival (OS) demonstrated significant differences between patients with MSI-H tumors and those with MSI-low (MSI-L) or microsatellite stable (MSS) tumors. The 5-year DFS rate was 78.0% in MSI-H patients and 69.9% in MSI-L/MSS patients (hazard ratio [HR], 0.84; 95% confidence interval [CI], 0.35-2.02; P = .689). The 5-year OS rates for MSI-H and MSI-L/MSS patients were 84.0% and 83.1%, respectively (HR, 0.86; 95% CI, 0.27-2.69; P = .790). By multivariate analysis, the MSI status did not affect either the DFS (HR, 1.00; 95% CI, 0.40-2.47; P = .994) or OS (HR, 0.85; 95% CI, 0.26-2.73; P = .778). ConclusionsMSI-H tumors are rarely observed in rectal adenocarcinoma, and the MSI status may not affect the survival outcome in patients with a resected rectal cancer.