Plasma clearance of RAS mutation under therapeutic pressure is a rare event in metastatic colorectal cancer
Résumé
In metastatic colorectal cancer (mCRC), circulating tumor 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. Patients with a RAS mutated tumor 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 at progression disease, we tested the methylation status of WIF1 and NPY genes using methylation-ddPCR (met-ddPCR) to validate the presence of ctDNA. Among 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. In conclusion, this 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. This article is protected by copyright. All rights reserved.
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