Circulating Cell-Free DNA from Colorectal Cancer Patients May Reveal High KRAS or BRAF Mutation Load

Florent Mouliere (1, 2) , Safia El Messaoudi (1, 2) , Celine Gongora (1) , Anne-Sophie Guedj (2) , Bruno Robert (1) , Maguy del Rio (1) , Franck Molina (2) , Pierre-Jean Lamy (3) , Evelyne Lopez-Crapez (3) , Muriel Mathonnet (4, 5) , Marc Ychou (1) , Denis Pezet (6) , Alain Thierry (1, 2)

1 IRCM - U896 Inserm - UM1 - Institut de recherche en cancérologie de Montpellier
2 SysDiag - Sysdiag-Modélisation et Ingénierie des Systèmes Complexes Biologiques pour le Diagnostic
3 Département d'oncologie Médicale
4 HCP - Homéostasie Cellulaire et Pathologies
5 Service d'Oncologie médicale [CHU Limoges]
6 CHU Clermont-Ferrand

We used a novel method based on allele-specific quantitative polymerase chain reaction (Intplex) for the analysis of circulating cell.free DNA (ccfDNA) to compare total ccfDNA and KRAS- or BRAF-mutated ccfDNA concentrations in blood samples from mice xenografted with the human SW620 colorectal cancer (CRC) cell line and from patients with CRC. Intplex enables single-copy detection of variant alleles down to a sensitivity of ≥0.005 mutant to wild-type ratio. The proportion of mutant allele corresponding to the percentage of tumor-derived ccfDNA was elevated in xenografted mice with KRAS homozygous mutation and varied highly from 0.13% to 68.7% in samples from mutation-positive CRC patients (n = 38). Mutant ccfDNA alleles were quantified in the plasma of every patient at stages II/III and IV with a mean of 8.4% (median, 8.4%) and 21.8% (median, 12.4%), respectively. Twelve of 38 (31.6%) and 5 of 38 (13.2%) samples showed a mutation load higher than 25%and 50%, respectively. This suggests that an important part of ccfDNA may originate from tumor cells. In addition, we observed that tumor-derived (mutant) ccfDNA was more fragmented than ccfDNA from normal tissues. This observation suggests that the form of tumor-derived and normal ccfDNA could differ. Our approach revealed that allelic dilution is much less pronounced than previously stated, considerably facilitating the noninvasive molecular analysis of tumors.

Domaines: Sciences du Vivant [q-bio]; Biologie cellulaire; Sciences du Vivant [q-bio]; Cancer

Florent Mouliere, Safia El Messaoudi, Celine Gongora, Anne-Sophie Guedj, Bruno Robert, et al.. Circulating Cell-Free DNA from Colorectal Cancer Patients May Reveal High KRAS or BRAF Mutation Load. Translational Oncology, 2013, 6 (3), pp.319 - 328. ⟨10.1593/tlo.12445⟩. ⟨hal-01826199⟩