Abstract 2134: Microsatellite instability status and high risk features in decision making for adjuvant chemotherapy in stage 2 colon cancer

Abstract

Abstract Background: The impact of adjuvant chemotherapy for patients with stage II colon cancer has been addressed in several clinical trials. NCCN guideline recommends that patients with stage II disease that is MSS/pMMR and at high risk for systemic recurrence can be considered adjuvant chemotherapy. However, research on whether these high-risk features or status of microsatellite instability (MSI) are predictive markers for adjuvant chemotherapy (ACT) is insufficient. Materials and Methods: We assessed the efficacy of ACT and possible interaction with MSI status and high-risk features for recurrence in patients with resected stage II colon diagnosed at 16 tertiary referral hospitals between January 2010 and December 2017. Results: According to MSI status, 394 patients (21.8%) had MSI-high tumors and 1416 (78.2%) had MSI-low or microsatellite stable (MSS) tumors. There were 881 patients (48.7%) with one or more high-risk feature for recurrence. Among 161 patients with MSI-high and high-risk features, the 5-year disease-free survival (DFS) and overall survival (OS) of patients who received no ACT, 5-FU chemotherapy, and oxaliplatin-based chemotherapy were 65.5% and 72.3%, 89.4% and 97.9%, and 88.2% 92.0%, respectively (DFS and OS: 5-FU vs. Oxaliplatin, p=0.972 and p=0.233, Oxaliplatin vs. no chemotherapy, p=0.016 and p=0.032, 5-FU vs. no chemotherapy, p=0.025 and p=0.003, respectively). Among 720 patients with MSI-low or MSS and high-risk features, the 5-year DFS and OS of patients who received no ACT, 5-FU, and oxaliplatin-based were 77.1% and 87.2%, 90.4% and 95.6%, and 86.9% 93.5%, respectively (DFS and OS: 5-FU vs. Oxaliplatin, p=0.580 and p=0.492, Oxaliplatin vs. no chemotherapy, p=0.037 and p=0.077, 5-FU vs. no chemotherapy, p=0.009 and p=0.012, respectively). In patients without risk factors, there was no benefit from ACT regardless of MSI status. Conclusions: 5-FU chemotherapy can be recommended in patients with one or more high-risk features for recurrence regardless of MSI status in stage II colon cancer. Keyword: Colonic Neoplasms, Adjuvant Chemotherapy, Microsatellite Instability, Risk Factors Citation Format: Sung Uk Bae, Woon Kyung Jeong, Seong Kyu Baek. Microsatellite instability status and high risk features in decision making for adjuvant chemotherapy in stage 2 colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2134.