De-scalation or swItch of Treatment According to Circulating tuMOr DNA Variation After 2 Cycles of Doublet Chemotherapy Plus Targeted Agent in Metastatic Unresectable Colorectal Cancer

Background : In unresectable mCRC, a de-escalation strategy using maintenance or chemotherapy (CT) discontinuation in selected cases is considered as a valid option in non-progressive patients after a first-line induction of doublet CT + targeted agent (TA) (1-7). In this context, circulating tumor DNA (ctDNA) is considered very promising to optimize decision making. Indeed, ctDNA harbour the same main alterations of the tumor and has been recognized as biologically relevant to reflect tumor dynamics and therapeutic efficacy (8). As reported in mCRC, that early variation of ctDNA during CT may be relevant to predict outcome (9-11). Indeed, patients with a ctDNA decrease from the first (C1) to the third (C3) cycles of CT (∆≥80% or ctDNA\<0.1 ng/ml at C3) or without ctDNA detectable at C1 and C3 have significant better survival as compared to patients with less decrease or with ctDNA increase (10). ctDNA monitoring had never been prospectively evaluated to guide early adaptation in the treatment strategy in mCRC. Aim: A randomized phase III, open label, strategy trial of the superiority in overall survival (OS) adjusted on quality of life of an early treatment adaptation guided by ctDNA variation versus a standard management in unresectable left-side, MSS-BRAFV600E non-mutated mCRC treated by first-line doublet CT + TA. Patients and methods : -Main inclusion criteria will be (i) unresectable left-side and non-pre-treated mCRC (ii) MSS and non-mutated BRAFV600E tumor (iii) at least one measurable lesion (iv) ECOG 0-1 and adequate biological functions for first-line doublet CT + TA (antiEGFR if RAS WT, bevacizumab (BV) if RAS MUT). Randomization (1:1) between an experimental strategy guided by ctDNA variation with de-escalation (Arm A1 or A2) or switch of treatment (Arm A3) versus standard strategy (Arm B). The analysis of variation of ctDNA from C1-C3 will be centralized and detected using Digital PCR targeting hypermethylation of WIF1/NPY genes (10) in real-time