P3.12 Circulating Dna Analysis in The Era of Personalized Cancer Medicine: Application to Kras/Braf Point Mutations Detection in Colorectal Cancer

Abstract

ABSTRACT Circulating DNA (ctDNA) analysis constitutes a hopeful approach to provide a non-invasive test potentially allowing diagnosis, prognosis, theranostics, therapeutic monitoring and follow-up in cancer patients. We studied tumour-derived ctDNA by an original approach focusing on its size distribution. We observed that tumour-derived ctDNA is mainly of size below 100 bp and exhibits a specific size distribution profile compared to healthy subjects [ 1 , 2 ]. Based upon these discoveries, we set up a refined allele-specific Q-PCR based method termed Intplex and adapted it to detect the 6 more frequent KRAS mutations in colorectal cancer (CRC) and the BRAFV600E point mutation [ 3 ]. In a single step, it determines simultaneously the ctDNA concentration, the ctDNA fragmentation, the mutational status and the mutation load (% mutant ctDNA from the total). Intplex sensitivity is 0.01% appearing unprecedented among Q-PCR-based methods. We reported higher plasma ctDNA concentrations and fragmentation levels in CRC patients than in healthy individuals 2 . Proof of concept of point mutation detection by Intplex was given by the full agreement of the results obtained on a cohort of 15 CRC patients between ctDNA analysis and tumour tissue analysis. Concordance of the mutational status determined by the two analyses examined in a clinical study on a cohort of 79 metastatic CRC patients will be presented [ 4 ]. This is the first blinded prospective study to compare KRAS and BRAF mutational status data obtained from the analysis of tumor tissue by routine gold standard methods and of plasma DNA using a novel method. Examination of the mutation load in a cohort of 48 mutated clinical samples from CRC patients revealed a wide inter-individual variation as values extended from 0.037% to 68.8% [ 5 , 6 ]. The opportunity in detecting quantitatively and dynamically mutation could constitute a non-invasive attractive tool for therapeutic monitoring and patient follow-up and expand the scope of personalized cancer medicine.