Background: In non-metastatic colorectal cancer (CRC), we evaluated prospectively the pertinence of longitudinal detection and quantification of circulating tumor DNA (ctDNA) as a prognostic marker of recurrence.
Method: The presence of ctDNA was assessed from plasma collected before and after surgery for 184 patients classified as stage II or III and at each visit during 3-4 years of follow-up. The ctDNA analysis was performed by droplet-based digital polymerase chain reaction, targeting mutation and methylation markers, blindly from the clinical outcomes. Multivariate analyses were adjusted on age, gender, stage, and adjuvant chemotherapy.
Results: Before surgery, 27.5% of patients were positive for ctDNA detection. The rate of recurrence was 32.7% and 11.6% in patients with or without detectable ctDNA respectively (P = 0.001). Time to recurrence (TTR) was significantly shorter in patients with detectable ctDNA before (adjusted hazard ratio [HR] = 3.58, 95% confidence interval [CI] 1.71-7.47) or immediately after surgery (adjusted HR = 3.22, 95% CI 1.32-7.89). The TTR was significantly shorter in patients with detectable ctDNA during the early postoperative follow-up (1-6 months) (adjusted HR = 5, 95% CI 1.9-12.9). Beyond this period, ctDNA remained a prognostic marker with a median anticipated diagnosis of recurrence of 13.1 weeks (interquartile range 28 weeks) when compared to imaging follow-up. The rate of ctDNA+ might be underestimated knowing that consensus pre-analytical conditions were not described at initiation of the study.
Conclusion: This prospective study confirms the relevance of ctDNA as a recurrence risk factor in stage II and III CRC before surgery and as a marker of minimal residual disease after surgery that may predict recurrence several months before imaging techniques.
Keywords: Circulating tumor DNA; Colorectal cancer; Liquid biopsy; Methylated DNA; Picodroplet droplet-based digital PCR; Prognostic marker.
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