623P - Plasma clearance of RAS mutation under therapeutic pressure is a rare event in metastatic colorectal cancer

Abstract

BackgroundIn metastatic colorectal cancer (mCRC), circulating tumour DNA (ctDNA) monitoring can be used to genotype tumors and track clonal evolution. We investigated the clearance of RAS mutated clones under chemotherapy pressure by ctDNA analysis in patients with a RAS mutated mCRC. MethodsPatients with a RAS mutated tumour included in the prospective PLACOL study, were monitored for ctDNA. Analyzes were based on optimized targeted next generation sequencing and/or droplet-based digital PCR (ddPCR). For plasma samples without detectable mutations, we tested the methylation status of WIF1 and NPY genes using methylation-ddPCR (met-ddPCR) to validate the presence of ctDNA. ResultsAmong the 36 patients with positive plasma samples for RAS mutations at inclusion, 28 (77.8%) remained RAS positive at disease progression, and 8 (22.2%) became negative. Subsequent met-ddPCR for methylated markers showed that only 2 out of the 8 patients with RAS negative plasma had detectable ctDNA at progression. Therefore, only two samples among 36 were confirmed for clearance of RAS mutation in our series. ConclusionsThis study suggests that the clearance of RAS mutations in patients treated by chemotherapy for a RAS mutated mCRC is a rare event. Monitoring tumor mutations in plasma samples should be combined with a strict control of the presence of ctDNA. The therapeutic impacts of RAS clearance need to be further explored. Legal entity responsible for the studyThe authors. FundingThe Ministère de l’Enseignement Supérieur et de la Recherche, the Université Paris-Descartes, the Centre National de la Recherche Scientifique (CNRS), the Institut National de la Santé et de la Recherche Médicale (INSERM), the Institut National du Cancer (INCA, n° 2009-1-RT-03-US-1 and 2009-RT-03-UP5-1), the Association pour la recherche contre le cancer (ARC, no. SL220100601375), the Agence Nationale de la Recherche (ANR Nanobiotechnologies; no. ANR-10-NANO-0002-09), the SIRIC CARPEM, the ligue nationale contre le cancer (LNCC, Program “Equipe labelisée LIGUE”; no. EL2016.LNCC/VaT) and Advanced Merieux Research Grant and canceropole funding (no. 2011-1-LABEL-UP5-2). DisclosureH. Blons: Advisory / Consultancy: AstraZeneca; Advisory / Consultancy: Merck; Advisory / Consultancy: Amgen; Advisory / Consultancy: Boehringer Ingelheim; Advisory / Consultancy: Pfizer. V. Taly: Advisory / Consultancy: Servier; Advisory / Consultancy: Boehringer Ingelheim; Advisory / Consultancy: Raindance Technologies. W. Shu-Fang: Research grant / Funding (institution): Servier. S. Pernot: Advisory / Consultancy: Amgen; Advisory / Consultancy: Sanofi. J. Taieb: Advisory / Consultancy, Speaker Bureau / Expert testimony: Merck; Advisory / Consultancy, Speaker Bureau / Expert testimony: Roche; Advisory / Consultancy, Speaker Bureau / Expert testimony: Amgen; Advisory / Consultancy, Speaker Bureau / Expert testimony: Eli Lilly; Advisory / Consultancy, Speaker Bureau / Expert testimony: Sanofi; Advisory / Consultancy, Speaker Bureau / Expert testimony: Celgene; Advisory / Consultancy, Speaker Bureau / Expert testimony: Sirtex; Advisory / Consultancy, Speaker Bureau / Expert testimony: Shire; Advisory / Consultancy, Speaker Bureau / Expert testimony: MSD; Advisory / Consultancy, Speaker Bureau / Expert testimony: Servier; Advisory / Consultancy, Speaker Bureau / Expert testimony: Pierre Fabre. P. Laurent-Puig: Advisory / Consultancy: Amgen; Advisory / Consultancy: Merck-Serono; Advisory / Consultancy: Sanofi; Advisory / Consultancy: Boehringer Ingelheim; Advisory / Consultancy: Roche; Advisory / Consultancy: Lilly. A. Zaanan: Advisory / Consultancy: Amgen; Advisory / Consultancy: Baxter; Advisory / Consultancy: Lilly; Advisory / Consultancy: Merck-Serono; Advisory / Consultancy: MSD; Advisory / Consultancy: Sanofi; Advisory / Consultancy: Roche; Advisory / Consultancy: Servier. All other authors have declared no conflicts of interest.