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 in arm A and in second step in arm B. Randomization in Arm A: after 4 cycles of doublet + TA, non-progressive patients will be allocated to a strategy according to ctDNA value and variation from C1-C3: Arm A1: CT discontinuation (ctDNA normalization \< 0.1 ng/ml or ctDNA not detectable) Arm A2 : maintenance with fluoropyrimidine + TA (ctDNA ≥ 0.1 ng/ml and ∆ctDNA≥ 80%). Arm A3 : ctDNA non-responders (∆ctDNA \< 80% or increase) : switch of CT +/- TA. Randomisation in Arm B: at least 8 cycles of doublet CT + TA before adaptation of sequence at physician choice. Statistical considerations : with an expected median OS at 32 months (mean 37.6 months), a mean QoL at 70.0% in first-line mCRC, corresponding to 0.700 x 37.6 = 26.3 QALM or 2.19 QALY (SD 1.18 QALY), 408 patients are required (randomization 1:1) to show a gain of 4 months of quality-adjusted OS (4 QALM or 0.33 QALY) in experimental ctDNA strategy versus standard strategy (5% two-sided type I error rate, 81% power and 1.18 QALY SD). The secondary objectives will be: * To compare strategies (standard vs ctDNA guided) overall and in the subgroups of ctDNA response on 18, 24 and 36-months restricted mean of QoL-adjusted OS, OS, PFS, response rate, toxicity, Quality of Life and cost utility. * Bio-collection for further ctDNA analysis. Only cost of samples collection and their transportation to the resource center is requested. Further ancillary analysis will be subject to independent funding requests to evaluate : * ctDNA kinetics during the induction and its impact on outcome in overall population and in each arm * ctDNA changes between time points during de-escalation arms to determine thresholds of variations predictive of clinical and/or radiological progression. Conclusion: DIAMOND is a randomized phase III strategy trial to show the superiority in OS adjusted on quality of life of an early treatment adaptation guided by ctDNA versus a standard management in unresectable left-side, MSS-BRAFV600E non-mutated mCRC treated by first-line doublet CT + TA.

NCT Number	NCT06446557
Lead Sponsor	University Hospital, Rouen
Conditions	Metastatic Colon Cancer
Enrollment	408 participants
Start Date	2026-06
Primary Completion	2032-06-01 (estimated)
Study Completion	2032-06-01 (estimated)
Updated on ClinicalTrials.gov	2026-06-09