The Prognostic Impact of Microsatellite Instability on the Outcome of Appendiceal Adenocarcinoma: a National Cancer Database Analysis

Abstract

BackgroundMicrosatellite instability (MSI) is recognized as a favorable outcome predictor in colorectal cancer. However, its impact on overall survival (OS) of appendiceal carcinoma has not been thoroughly studied. This study aimed to assess the impact of MSI on OS of patients with appendiceal adenocarcinoma, stratified by disease stage, tumor histology, and patients’ demographics. MethodsThis was a retrospective cohort analysis of the colon cancer National Cancer Database (NCDB) between 2005 and 2019. Patients with appendiceal adenocarcinoma with known MSI status were included and subdivided according to MSI status into positive and negative. Primary outcome was OS stratified by MSI status. ResultsThe study included 1681 (50.1% male) patients with a mean age of 58.9±14.2 years; 211 (12.5%) had MSI-positive tumors (69 MSI low, 53 MSI high, and 89 not specified). Mean 5-year OS of patients with MSI-positive and MSI-negative carcinomas was similar (81.9 versus 78.6 months, p = 0.747). Patients with stage IV MSI-positive carcinomas had significantly longer OS than patients with MSI-negative carcinomas of the same stage (41.3 vs 26.5 months, p = 0.02). Differences in OS for patients with stages I–III were not statistically significant. Compared to MSI-negative/low carcinomas, MSI-high tumors had more advanced pathologic TNM stage (stage III: 23.9% vs 17.8%—stage IV: 41.3% vs 35.4%, p = 0.003), received more chemotherapy (56% vs 41%, p = 0.04), yet had similar OS (81.9 vs 78.9 months, p = 0.357). ConclusionsMSI status of appendiceal adenocarcinomas did not significantly impact survival, except for stage IV disease in which a survival benefit of MSI was noted.