SUMMARY: Adjuvant treatment decisions in stage III colon cancer (CC) have traditionally relied on TNM staging to classify patients as low risk (T1-3N1) or high risk (T4 and/or N2) following surgery. However, outcomes remain highly variable despite standard adjuvant treatment with CAPOX or FOLFOX. The IDEA collaboration highlighted this heterogeneity, with 5-year disease-free survival (DFS) ranging from nearly 90% in T1N1a tumors to approximately 31% in T4N2b disease.
Circulating tumor DNA (ctDNA) has emerged as a promising biomarker for detecting molecular residual disease (MRD) after surgery. Detectable postoperative ctDNA may identify patients harboring persistent microscopic disease and refine recurrence risk beyond conventional staging alone.
N0147 Trial Highlights Prognostic Value of ctDNA
A recent analysis of the Phase III Alliance/NCCTG N0147 trial evaluated postoperative plasma samples from 2,260 patients with resected Stage III colon cancer using Guardant Reveal, a tissue-free epigenomic ctDNA assay.
Approximately 20% of patients were ctDNA-positive after surgery. ctDNA positivity was more common in tumors with adverse pathologic features, including:
- T4 disease
- N2 nodal involvement
- High-grade histology
- Bowel obstruction or perforation
- BRAFV600E mutations
The highest ctDNA positivity rates were observed in patients with bowel perforation.
ctDNA Positivity Strongly Predicts Recurrence and Survival
At a median follow-up exceeding six years, postoperative ctDNA positivity was associated with significantly worse outcomes across all major endpoints:
- Shorter Disease-Free Survival (DFS) – Hazard Ratio=5.03
- Reduced Time To recurrence (TTR) – Hazard Ratio=5.96
- Poorer Overall Survival (OS) – Hazard Ratio=4.45
Five-year DFS was 27.7% in ctDNA-positive patients versus 77.1% in ctDNA-negative patients, while 5-year OS was 50.4% versus 86.8%, respectively. Importantly, ctDNA remained an independent prognostic factor after adjustment for clinicopathologic variables:
These findings suggest ctDNA may more accurately identify patients with persistent residual disease following surgery than TNM staging alone.
Redefining “Low-Risk” Disease
The adverse prognostic impact of ctDNA positivity was particularly pronounced in patients traditionally considered lower risk, including:
- T1/T2 tumors
- N1 disease
- Clinically “low-risk” Stage III disease
- Deficient MisMatch Repair (dMMR) tumors
These findings highlight limitations of conventional staging and suggest that molecular residual disease can exist even in anatomically favorable tumors.
Epigenetic Tumor Fraction Adds Prognostic Precision
Investigators also evaluated epigenetic Tumor Fraction (TF), a quantitative measure of residual tumor burden. Among ctDNA-positive patients, higher TF levels correlated with:
- Increased recurrence risk
- Shorter DFS
- Inferior Overall Survival
These results align with findings from studies such as DYNAMIC and GALAXY, supporting the concept that ctDNA quantity, not simply detectability, may further refine recurrence risk assessment.
Molecular Profiling and Patterns of Recurrence
ctDNA-positive patients were more likely to develop liver metastases, while ctDNA-negative relapses more commonly involved locoregional or peritoneal recurrence.
Genomic profiling of ctDNA-positive samples identified recurrent mutations in FLT1 (VEGFR1), PREX2, KRAS, BRAF, ATM, BRCA2 and PIK3CA.
Notably, FLT1 and PREX2 demonstrated strong associations with recurrence risk, highlighting potential future opportunities for MRD-directed precision therapies.
Is ctDNA Ready to Guide Treatment Decisions?
Despite its strong prognostic value, ctDNA is not yet fully established as a treatment-directing biomarker. Trials evaluating ctDNA-guided treatment escalation have produced mixed results, and persistent ctDNA positivity after standard chemotherapy remains common, indicating that current adjuvant regimens may be insufficient to eradicate molecular residual disease in many patients.
Currently, ctDNA appears most valuable as a complementary risk stratification tool integrated with TNM staging, Mismatch repair status, Molecular profiling and traditional high-risk clinicopathologic features.
Ongoing studies, including CIRCULATE-US and other MRD-directed trials, aim to clarify whether ctDNA-guided treatment strategies can improve outcomes.
Looking Ahead
ctDNA testing has the potential to reshape postoperative colon cancer management through:
- Personalized adjuvant therapy selection
- Risk-adapted surveillance strategies
- Earlier relapse detection
- Integration with precision oncology approaches
Tissue-free assays may further support broader clinical adoption by eliminating the need for tumor tissue sequencing and streamlining workflow.
Conclusion
The N0147 analysis represents one of the largest evaluations of tissue-free MRD assessment in resected Stage III colon cancer. Postoperative ctDNA positivity emerged as a powerful independent predictor of recurrence and survival, refining prognostic assessment beyond traditional TNM staging.
Although ctDNA is not yet ready to direct treatment decisions independently, it is increasingly positioned as an important complementary biomarker in precision oncology and may ultimately play a central role in individualized postoperative management of colon cancer.
Tissue-Free Circulating Tumor DNA Assay and Patient Outcome in a Phase III Trial of FOLFOX-Based Adjuvant Chemotherapy (Alliance N0147). Sinicrope FA, Segovia D, Sharma N, et al. J Clin Oncol. 2026;44:1401-1415
