Koenig JL, et al. - Researchers investigated the effectiveness of adjuvant chemotherapy (ACT) in stage II colon cancer (CC) patients with known microsatellite instability (MSI) status from the National Cancer Database. In addition, they sought for the possible interaction with MSI status and tumor sidedness. They identified 6,964 stage II CC patients with known MSI status; of these, 1,497 (21.5%) received ACT, 843 had MSI tumors, and 6,121 had microsatellite stable (MSS) tumors. After adjusting for factors including high-risk features, MSI status, and tumor sidedness, multivariate and propensity score matched analyses suggested ACT to be associated with improved survival. No interaction between receipt of ACT and MSI status was evident. ACT was identified as beneficial for patients with MSS tumors, even without other high-risk features. but it was not for patients with MSI tumors. Tumor sidedness did not influence ACT induced improved survival.