Abstract 2632: Clinical validation of circulating DNA analysis for the detection of point mutations and of the longitudinal metastatic colorectal patient follow up for detecting emergence of resistance to targeted therapy
Authors: Thierry Alain R. , El Messaoudi Safia , Mollevi Caroline , Pastor Brice , Sanchez Cynthia , Raoul Jean-Luc , Guimbaud Rosine , Pezet Denis , Artru Pascal , Mathonnet Muriel , De La Fouchardiere Christelle , Borg Christophe , Assenat Eric , Bouche Olivier , Gavoille Céline , Kopetz Scott , Ychou Marc 
Published: July 2016

Abstract
Clinical validation of circulating DNA analysis as liquid biopsy for the detection of point mutations and of the longitudinal metastatic colorectal patient follow up for detecting emergence of resistance to targeted therapy
We carried out two clinical studies in metastatic colorectal cancer patients (i) the clinical real-time evaluation of circulating tumor DNA (ctDNA) analysis for detecting point mutations in comparison with tumor tissue analysis before initiation of anti-EGFR therapy and (ii), the study of the emergence of associated resistance mutation in refractory patients under treatment.
(i) We realized a real-time blinded prospective multicentric clinical study on 140 patients comparing KRAS (exon 2,3 and 4) and BRAF V600E mutations determination by plasma and tissue analysis carried out in the conditions of standard management care. On 121 patients where both analysis were made, 43% were found mutant by tumor tissue analysis while 57% were found KRAS mutant by ctDNA analysis. 7.2% of patients were found BRAF mutant by tumor tissue while 14.4% were determined mutant by ctDNA analysis. 13% of plasma samples carried multiple KRAS point mutations and 4% of plasma samples exhibited at least one KRAS point mutation combined to the presence of BRAFV600E point mutation. Median data turnaround time was 16 [3-273] days for tumor tissue while it was 2 [0.5-10] days for ctDNA analysis. CtDNA analysis appears much more sensitive than tissue analysis and may be more accurate in respect to the intra-tumor or inter-tumor heterogeneity and the clonal evolution dynamics. We present the first RAS and BRAF mutation distribution which takes into account the presence of multiple mutations in the same mCRC patient.
(ii) In the other blinded clinical study, we retrospectively analyzed RAS (KRAS and NRAS) and BRAF mutations in serial plasma samples from 42 refractory mCRC patients to Folfox + cetuximab or dasatinib. 98% of the plasma were found mutant before or during treatment. 50% of KRAS mutant samples were missed by tumor tissue analysis before treatment. 4.8% of patients were found BRAF mutant by tumor tissue analysis while 7% were found mutant by ctDNA analysis. Longitudinal plasma analysis shows that 80% of initially WT patients acquire at least one RAS or BRAF mutation during treatment and that 38% of initially mutant patients acquire at least one newly KRAS or BRAF point mutation during treatment. CtDNA analysis allows tracking acquired resistance by studying the real-time clonal evolution of the tumor
Patients may harbor mutations at very low frequency on ctDNA down to 0.01% before initiation or during treatment revealing the need of a high sensitive technique to detect mutant subclones. Our results indicate that plasma analysis could advantageously replace tumor tissue analysis and enables longitudinal examination of tumor molecular profiling.
Citation Format: Alain R. Thierry, Safia El Messaoudi, Caroline Mollevi, Brice Pastor, Cynthia Sanchez, Jean-Luc Raoul, Rosine Guimbaud, Denis Pezet, Pascal Artru, Muriel Mathonnet, Christelle De La Fouchardiere, Christophe Borg, Eric Assenat, Olivier Bouche, Céline Gavoille, Scott Kopetz, Marc Ychou. Clinical validation of circulating DNA analysis for the detection of point mutations and of the longitudinal metastatic colorectal patient follow up for detecting emergence of resistance to targeted therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2632.