Validation of a next-generation sequencing assay for the detection of EGFR mutations in cell-free circulating tumor DNA.

Detection of EGFR mutations from blood plasma represents a gentle, non-invasive alternative to rebiopsy and can therefore be used for therapy monitoring of non-small-cell lung cancer (NSCLC) patients. The aim of this project was to investigate whether the Reveal ctDNA™ 28 NGS assay (ArcherDX, Boulder, CO), has a comparable sensitivity and specificity to droplet digital PCR (ddPCR, gold-standard) and is therefore suitable for therapy monitoring of progressing lung cancer patients. First, we validated the NGS assay with a commercially available reference material (SeraCare, Massachusetts, US). Using an input of 22 ng, a sensitivity of 96% and a specificity of 100% could be achieved for variant allele frequencies (VAF) of 0.5%. For variants at a VAF of 0.1% the sensitivity was substantially reduced. Next, 28 plasma samples from 16 patients were analyzed and results were compared to existing ddPCR data. This comparative analysis of patient samples revealed a concordance of 91% between NGS and ddPCR. These results confirm that the Reveal ctDNA™ 28 NGS assay can be used for therapy monitoring of patients under TKI therapy. However, due to the slightly superior sensitivity of ddPCR, a combination of NGS (with broad coverage of a large number of genomic loci) and ddPCR (with targeted highly sensitive detection of specific mutations) might be the ideal approach.