Computed tomography-dominant surveillance strategies for colorectal cancer: Improving early detection of recurrence

Table 1 Advantages, disadvantages, and potential improvements for colorectal cancer surveillance modalities

Modality	Advantages	Disadvantages	Potential areas for improvement
CT scans	High sensitivity for detecting distant metastases (88.9% diagnostic yield)[16]. Non-invasive, widely available[6]. Effective for both local and systemic recurrence[17]	Radiation exposure, particularly cumulative risk in younger patients[6]. Variability in protocols (e.g., contrast use, slice thickness) affects sensitivity[16]	Implement low-dose CT protocols to reduce radiation while maintaining sensitivity[6]. Standardize imaging protocols (e.g., thin-slice, contrast-enhanced) for consistent detection[16]
Colonoscopy	Direct visualization and biopsy capability for local recurrence and metachronous neoplasms[16]. High specificity for colorectal lesions[12]. Allows therapeutic intervention (e.g., polyp removal)[11]	Invasive, requiring sedation and bowel preparation[12]. Low detection rate for distant metastases (4.6%)[16]. Patient discomfort and adherence barriers[18]	Enhance patient education and preparation to improve adherence[19]. Prioritize high-risk patients using ctDNA to reduce unnecessary procedures[20]. Explore less invasive alternatives (e.g., virtual colonoscopy)[6]
Tumor markers (CEA, CA19-9, ctDNA)	Non-invasive, repeatable testing[21]. ctDNA offers high sensitivity for minimal residual disease (HR: 17.5 for recurrence)[14]. Guides risk-stratified surveillance[20].	Low sensitivity for CEA/CA19-9 (about 40% of recurrences missed, especially lung)[21,22]. False positives (e.g., CEA elevations in non-malignant conditions)[23]	Improve CEA/CA19-9 specificity via machine learning (e.g., microRNA integration)[24]. Standardize ctDNA protocols and reduce costs through subsidized programs[20]. Validate ctDNA in diverse populations to minimize false positives[14]

CEA: Carcinoembryonic antigen; ctDNA: Circulating tumor DNA; HR: Hazard ratio; CA19-9: Carbohydrate antigen 19-9; CT: Computed tomography.

Table 2 Risk-adapted surveillance strategy for postoperative stage I-III colorectal cancer patients

Risk category	Imaging (CT/MRI)	Colonoscopy	Biomarker testing (CEA)	Rationale
High-risk (e.g., stage III, MSS, positive biomarkers)	Every 6 months for years 1-3, annually for years 4-5 (low-dose protocols for patients < 50)	At 1 year post-surgery, then every 3 years if negative	Every 3 months for 3 years, then every 6 months	Higher recurrence risk justifies intensive imaging, balanced with low-dose CT to reduce radiation exposure[6,10,12]
Intermediate-Risk (e.g., stage II, MSS, negative biomarkers)	Annually for years 1-3, every 2 years for years 4-5 (MRI preferred for patients < 50)	At 1 year, then every 3-5 years if negative	Every 6 months for 3 years, then annually	Moderate risk warrants regular but less frequent imaging, with MRI to minimize radiation in younger patients[10,12]
Low-risk (e.g., stage I, MSI-H, negative biomarkers)	Every 2 years for years 1-5 (MRI or low-dose CT for patients < 50)	At 1 year, then every 5 years if negative	Annually for 5 years	Lower recurrence risk supports extended intervals, prioritizing radiation reduction[6,10,12]

MSS: Microsatellite stable; MSI-H: Microsatellite instability-high; CEA: Carcinoembryonic antigen; MRI: Magnetic resonance imaging; CT: Computed tomography.