The Role of Adjuvant Chemotherapy in High-Risk Stage II Colon Cancer with Microsatellite Instability-High or DNA Mismatch Repair Deficiencies: A Multicenter Pooled Analysis (KCSG-CO24-03)
Year: 2026
Type: article
Abstract: Purpose: The benefit of adjuvant chemotherapy (CTx) for high-risk stage II microsatellite instability-high (MSI-H)/mismatch repair deficient (dMMR) colon cancer remains controversial with discordant international guidelines. This study evaluated outcomes comparing adjuvant chemotherapy group versus surgery only group. Materials and Methods: This multicenter retrospective analysis included 192 patients with high-risk stage II MSI-H/dMMR colon cancer who underwent curative resection between 2010 and 2020. High-risk features included pT4, grade 3-4, lymphovascular invasion, bowel obstruction/perforation, perineural invasion (PNI), inadequate lymph node sampling (<12), or close margins. The primary endpoint was 5-year relapse-free survival (RFS), excluding second primary malignancies to isolate antitumor efficacy. Results: Of 192 patients, 128 (66.7%) received adjuvant CTx and 64 (33.3%) underwent observation (median follow-up 60.5 months). Five-year RFS (94.0% vs. 83.7%; p=0.001) and OS (98.3% vs. 89.0%; p=0.001) were significantly higher with adjuvant CTx. Multivariate analysis confirmed adjuvant CTx as an independent predictor for RFS (HR 0.249, 95% CI 0.109-0.571; p=0.001) and OS (HR 0.155, 95% CI 0.051-0.470; p=0.001). PNI was also identified as a significant independent predictor of RFS (HR, 3.581; 95% CI, 1.529 to 8.387; p=0.003) and OS (HR, 4.968; 95% CI, 1.654 to 14.930; p=0.004). CTx-related toxicities were clinically manageable, and no treatment-related deaths were reported. Conclusion: Adjuvant CTx significantly improves RFS and OS in high-risk stage II MSI-H/dMMR colon cancer, particularly in pT4 and PNI patients. These findings provide evidence to bridge NCCN and ESMO guideline discrepancies, supporting risk-stratified adjuvant CTx in this population.
Source: Cancer Research and Treatment
Institutions: Asan Medical Center, University of Ulsan, National Cancer Center, Ulsan University Hospital, Dankook University Hospital, Dankook University, The Catholic University of Korea Seoul St. Mary's Hospital, Catholic University of Korea, Soonchunhyang University Hospital Bucheon, Ajou University Hospital, Ajou University, Pusan National University Yangsan Hospital, Pusan National University, Yonsei Cancer Hospital, Jeonbuk National University Hospital, Jeonbuk National University, Jeju National University Hospital, Jeju National University, Chung-Ang University Hospital, Chung-Ang University, Kyungpook National University, Chonnam National University Hwasun Hospital
Language: English
Subfield: Pathology and Forensic Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
Funder: Hanyang University
OpenAlex ID: W7162693997
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