Copyright: ©Author(s) 2026. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution-NonCommercial (CC BY-NC 4.0) license. No commercial re-use. See permissions. Published by Baishideng Publishing Group Inc.
World J Gastrointest Oncol. Nov 15, 2026; 18(11): 123709
Published online Nov 15, 2026. doi: 10.4251/wjgo.123709
Published online Nov 15, 2026. doi: 10.4251/wjgo.123709
Clinical and molecular heterogeneity of microsatellite instability-high colorectal cancer in older adults
Tatsuya Shonaka, Chikayoshi Tani, Shoichiro Mizukami, Daisuke Koro, Hiroyoshi Iwata, Mizuho Ohara, Hideki Yokoo, Division of Gastroenterological and Transplantation Surgery, Department of Surgery, Asahikawa Medical University, Asahikawa 078-8510, Japan
Hiroki Tanabe, Division of Gastroenterology, Department of Internal Medicine, Asahikawa Medical University, Asahikawa 078-8510, Japan
Hiroki Tanabe, Yoshio Makita, Department of Genetic Counseling, Asahikawa Medical Univer
Mishie Tanino, Department of Pathology, Asahikawa Medical University Hospital, Asahikawa 078-8510, Japan
Author contributions: Shonaka T, Tani C, and Mizukami S contributed to study conception and design; Koro D, Iwata H, and Ohara M collected and analyzed data; Tanabe H and Makita Y provided genetic counseling and advice; Tanino M performed pathological diagnosis and mismatch repair immunostaining for pathological evaluation; Shonaka T wrote the first draft of this manuscript; Yokoo H supervised the study. All the authors critically reviewed, commented on, and approved the final manuscript.
AI contribution statement: Portions of this manuscript were edited using AI tools (specifically Gemini) solely for language refinement. The authors carefully reviewed and verified all AI-assisted outputs and take full responsibility for the scientific content of the manuscript.
Supported by Akiyama Life Science Foundation.
Institutional review board statement: The study was reviewed and approved by the Ethics Committee of Asahikawa Medical University, No. 24011.
Informed consent statement: Informed consent was obtained from all patients via an opt-out framework, in accordance with the institutional ethical requirements and the Declaration of Helsinki. Patient data were fully anonymized to protect personal information.
Conflict-of-interest statement: All the authors report no relevant conflicts of interest for this article.
STROBE statement: The authors have read the STROBE Statement-checklist of items, and the manuscript was prepared and revised according to the STROBE Statement-checklist of items.
Data sharing statement: The datasets supporting the conclusions of this study are available from the corresponding author upon request. Owing to ethical and confidentiality constraints, the raw datasets are not publicly available.
Corresponding author: Tatsuya Shonaka, MD, PhD, Division of Gastroenterological and Transplantation Surgery, Department of Surgery, Asahikawa Medical University, 2-1 Midorigaoka-Higashi, Asahikawa 078-8510, Japan. shonaka@asahikawa-med.ac.jp
Received: May 27, 2026
Revised: June 26, 2026
Accepted: July 16, 2026
Published online: November 15, 2026
Processing time: 154 Days and 4.7 Hours
Revised: June 26, 2026
Accepted: July 16, 2026
Published online: November 15, 2026
Processing time: 154 Days and 4.7 Hours
Core Tip
Core Tip: While microsatellite instability-high colorectal cancer in older adults is widely considered sporadic, our real-world data revealed that 28.6% (6/21) of older adults with microsatellite instability-high exhibited atypical molecular profiles, including BRAF wild-type/MLH1 and MSH2/MSH6 deficiencies. Age-based assumptions can lead to missed diagnoses of Lynch syndrome, as demonstrated in the 72-year-old patient in our study. Therefore, reflex MLH1 promoter methylation analysis should be routinely performed regardless of age to optimize precision medicine and facilitate life-saving cascade screening of family members.