MEDtalk HIGHLIGHTS

During ASCO GI 2023, Stacey Cohen, a medical oncologist at the Fred Hutchinson Cancer Center and University of Washington in Seattle, presented a study evaluating the detection of circulating tumor DNA (ctDNA) in patients with stage I to III colorectal cancer immediately after surgery. The study analyzed a database of 14,425 patients with at least one ctDNA result to investigate whether the increase in cell-free DNA (cfDNA) after surgery would impact the ability to detect ctDNA for minimal residual disease (MRD). The study concludes, that although cfDNA levels increased during the first two weeks after surgery, this rise did not interfere with detecting ctDNA for MRD, which remained reliable after approximately two weeks.

No impact of cfDNA

The frequency of ctDNA was highest during the first two weeks after surgery, but positivity decreased after eight weeks, likely due to adjuvant chemotherapy. The study also demonstrated that postoperative MRD or ctDNA positivity was a reliable predictor of recurrence-free survival, with the highest positivity in stage III and the lowest in MSIhigh tumors. Even though the multivariate analysis did not impact cfDNA concentration, MRD remained the most robust predictor of recurrence-free survival.

Conclusion

The study concluded that the elevation in cfDNA after surgery did not affect the ability to detect ctDNA for MRD, and standard emerge testing windows could start as early as two weeks after surgery. However, further research is needed to investigate the small number of patients who showed ctDNA positivity in the first week after surgery.

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