Prognostic Value and Relation with Adjuvant Treatment Duration of ctDNA in Stage III Colon Cancer: a Post Hoc Analysis of the PRODIGE-GERCOR IDEA-France Trial

{Purpose: Circulating tumor DNA (ctDNA) has been suggested as a major prognostic factor in resected stage-III colon cancer. We analyzed ctDNA of patients randomized in the phase III IDEA-France trial. Experimental Design: ctDNA was tested for WIF1 and NPY by droplet digital PCR with method developed and validated for colorectal cancer. Disease-free survival (DFS) and overall survival (OS) were analyzed via multivariable analysis in patients with ctDNA samples and in sub-groups according to treatment duration (3/6 months) and disease stage (high/low-risk stage III). Results: Of 2,010 randomized patients, 1,345 had available ctDNA samples (1,017 collected both post-surgery and prechemotherapy). More Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 (78% versus 69%) and T4 and/or N2 (40% versus 36%) were observed in patients studied (n = 1017) versus not analyzed (n = 993). There were 877 ctDNA-negative (86.2%) and 140 ctDNA-positive (13.8%) patients; their baseline characteristics were similar. With a median follow-up of 6.6 years, the 3-year DFS rate was 66.39% for ctDNA-positive patients and 76.71% for ctDNA-negative patients (P = 0.015). ctDNA was confirmed as an independent prognostic marker for DFS (adjusted HR = 1.55, 95% CI 1.13-2.12