Detection of somatic mutations in ctDNA derived from adenocarcinoma patients – EGFR tyrosine kinase inhibitor monitoring preliminary study

Aim of the study
The main purpose of this study was to assess detection of mutations in the epidermal growth factor receptor (EGFR) gene in circulating tumor DNA (ctDNA) as a tool for EGFR tyrosine kinase inhibitor (TKI) monitoring therapy.

Material and methods
The study was conducted using 20 samples from 7 adenocarcinoma patients treated with TKIs. Blood samples for ctDNA analysis were collected in 2015–2016. ctDNA was isolated using the QIAamp Circulating Nucleic Acid Kit (Qiagen) and analyzed using the ctEGFR Mutation Detection Kit (EntroGen).

Results
The most common exon 19 deletion and p.Leu858Arg mutation in exon 21 of the EGFR gene were detected. We observed a correlation between stabilization of patient condition and the lack of p.Thr790Met mutation detection in ctEGFR during TKI treatment (2 out of 7 patients). We also observed a correlation between progression of the disease and p.Thr790Met mutation detection in ctEGFR (3 out of 7 cases). We did not detect ctDNA p.Thr790Metp in two patients in whom progression occurred shortly thereafter. Last but not least, we noticed that good organization during plasma collection and transportation (average time of 6 minutes and 30 seconds) allows to use K2EDTA tubes.

Conclusions
When tissue is limited or insufficient, analysis of the ctEGFR mutational status can be considered as an alternative tool for qualifying patients with non-small cell lung cancer (NSCLC) for TKI therapy, also as a potential monitoring tool. The plasma p.Thr790Met-negative result needs to be verified for the presence of p.Thr790Met-positive tumor tissue.