Prognostic Impact of Microsatellite Instability in Asian Gastric Cancer Patients Enrolled in the ARTIST Trial

Background: Caucasian patients with microsatellite instability (MSI)-high gastric cancer (GC) may have better prognosis but worse outcomes. Objective: Here we explored the prognostic role of MSI in Asian patients. Methods: This post hoc analysis comprehended radically resected GC patients randomized to XP (capecitabine/cisplatin) or XPRT. MSI status was assessed by combining immunohistochemistry with multiplex polymerase chain reaction. The MSI prognostic effect on disease-free survival (DFS) and overall survival (OS) was evaluated. Results: 393 tissue samples were analyzed and 35 (9%) were MSI-high. This subgroup was characterized by: older age, Borrmann classification 1-2, antral localization, T3-4 stage, and intestinal type. At univariable analysis, the microsatellite-stable subgroup showed a trend toward a worse prognosis as compared to the MSI-high group: 3-year DFS was 76.3 versus 85.4% (p = 0.122); 3-year OS was 81.7 versus 91.4% (p = 0.046). Multivariable analyses confirmed it in both DFS (hazard ratio, HR = 2.32 [95% CI 0.91, 5.88]; p = 0.077) and OS (HR = 3.17 [95% CI 0.97, 10.43]; p = 0.057). Conclusions: MSI-high status was associated with specific clinical-pathological features and a trend toward better outcomes of Asian GC patients.