Circulating tumor DNA (ctDNA) analysis after surgery for colorectal cancer with liver metastases can identify patients who benefit from adjuvant chemotherapy, according to research presented at the ESMO Gastrointestinal Cancers Congress 2026. Findings from the GALAXY study indicate that patients with detectable ctDNA post-resection face a higher risk of recurrence, yet these same individuals show significantly improved survival rates when treated with chemotherapy.
How ctDNA Functions as a Biomarker
Circulating tumor DNA refers to small fragments of DNA shed by tumors into the bloodstream. In the context of colorectal cancer, detecting ctDNA after surgery serves as a marker for minimal residual disease—microscopic cancer cells that remain in the body despite successful surgical removal of visible tumors.
According to data from the GALAXY study, which followed 298 patients, the presence of ctDNA post-surgery is a strong predictor of clinical outcomes. Patients who tested positive for ctDNA after their initial surgery faced a risk of recurrence more than four times higher than those who tested negative. Furthermore, the risk of mortality was more than nine times higher for the ctDNA-positive group.
Impact of Adjuvant Chemotherapy
The study highlights a clear divergence in how patients respond to post-surgical treatment based on their ctDNA status. For patients with detectable ctDNA after surgery, chemotherapy provided a substantial clinical benefit.
Data from the four-year follow-up period showed:
- Overall Survival: 65% for patients who received chemotherapy compared to 33% for those who did not.
- Disease-Free Survival: 38% for the chemotherapy group versus 7% for the untreated group.
- Recurrence Risk: Chemotherapy was associated with a 93% reduction in the risk of cancer recurrence in this specific subgroup.
Conversely, patients who tested negative for ctDNA showed favorable outcomes regardless of whether they received additional chemotherapy. This suggests that ctDNA testing could eventually help clinicians spare low-risk patients from the unnecessary toxicities associated with chemotherapy, such as fatigue, neuropathy, and gastrointestinal complications.
Limitations and Clinical Context
While the GALAXY study results are promising, researchers and independent experts emphasize that ctDNA testing is not yet a standard of care for clinical decision-making.
Professor Per Pfeiffer, an oncologist at Odense University Hospital in Denmark, noted that while the potential to refine patient selection is significant, current evidence is not yet sufficient to mandate this practice in routine clinical settings. Furthermore, the study identified a specific limitation: the predictive value of ctDNA appeared different in patients who had received neoadjuvant chemotherapy (treatment before surgery). In this subgroup, additional chemotherapy after surgery did not improve clinical outcomes, regardless of the ctDNA test results. Researchers suggest that prior treatment may alter tumor biology, requiring further investigation into how these markers should be interpreted in patients with complex treatment histories.
Key Considerations for Future Treatment
The study, led by the Hyogo Medical University in Japan in collaboration with international partners including the University of Oxford, underscores a shift toward personalized oncology. By identifying who truly requires adjuvant treatment, medical teams aim to balance the necessity of aggressive therapy against the risks of overtreatment. Until further large-scale validation confirms these protocols, the use of ctDNA remains a subject of ongoing clinical research rather than established practice.
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