BACKGROUND: There is no significant difference in postoperative follow-up imaging examinations for varying mismatch repair (MMR)/microsatellite instability (MSI) statuses for sporadic colorectal cancer while facing different prognoses. METHODS: We conducted a retrospective study, using Kaplan-Meier curve to compare survival/progression status by varying imaging examination and frequency, using Cox regression to analyze tumor characteristic impact on survival, and monitoring polyp detection time in each colonoscopy screening. RESULTS: A total of 282 deficient MMR (dMMR)/MSI-high (MSI-H) patients were included. After a 7 year follow-up, all patients-including 143 examined by CT and colonoscopy, 86 singularly examined (CT/colonoscopy/ultrasound), and 53 received no imaging examination-demonstrated a favorable overall survival (87.97%, 95% CI 75.99-89.19) and disease-free survival (81.92%, 95% CI 70.38-89.30), which had no significant difference between imaging methods. Cox regression proved that different imaging methods had no influence on the prognosis. Stage III patients experienced a deterioration in disease-free survival but not differed between varying imaging methods. Different CT follow-up interval exhibited no difference in survival and progression. Polyps were detected in 39.75% (64/161) of patients during follow-up
32.81% (21/64) were detected in colonoscopy conducted 0-6 months after surgery, reaching the highest. For multiple polyps, the median of detection interval was 13-24 months (first and second polyps), 7-12 months (second and third polyps). CONCLUSIONS: For nonmetastatic dMMR/MSI-H sporadic colorectal cancer patients, less CT scans (interval >
1 year) are tolerable because of good prognosis, whereas more colonoscopy screenings (0-6 months after surgery first year
13-24 months after first polyps detection
7-12 months after second polyps detection) is considerable.