Abstract 1354P
Background
Detection of the EGFR T790M resistance mutation in NSCLC patients progressing on EGFR tyrosine kinase inhibitors (TKI) is mandatory because these patients will benefit from osimertinib treatment. In this context, the use of ctDNA is a very powerful approach, but a sensitive and specific method must be used. We report here the comparison of the Cobas® EGFR Mutation Test v2 kit (Roche®) and the digital PCR (dPCR) RESIST kit (ID-Solutions), for the detection of the T790M mutation in plasma of NSCLC patients.
Methods
ctDNA was extracted using 2 mL of EDTA plasma samples collected from NSCLC patients with the cfDNA Sample Preparation Kit (Roche®). Analysis was then performed using the Cobas® EGFR Mutation Test v2 on the Cobas® Z480 real time PCR system (Roche®) and the dPCR RESIST kit on the NaicaTM Crystal digital PCR system (Stilla Technologies). The limit of detection (LoD) of the RESIST kit was determined at 3 droplets by testing 18 negative plasma samples from melanoma or colon cancer patients.
Results
110 plasma samples, collected from NSCLC patients progressing on EGFR TKI and tested positive on plasma for an EGFR activating mutation using the Cobas® test, were included. With the Cobas® assay, the T790M mutation was detected in 20 samples (18.2%), 88 samples presented only the EGFR activating mutation (80.0%) and 2 tests (1.8%) were not contributive. Analysis of these 110 samples with the dPCR RESIST kit allowed us to identify 28 samples (25.5%; including the 20 samples that were Cobas® positive) containing the T790M mutation. 78 samples were T790M negative (70.9%), and 4 tests were not contributive (including the 2 samples that were not contributive by Cobas®). These results showed that dPCR using the RESIST kit allowed us to detect 8 additional T790M positive samples as compared to the Cobas® assay, yielding a negative percent agreement of 90.7%, and a positive percent agreement of 100%.
Conclusions
Digital PCR using the RESIST kit is more sensitive than the Cobas® assay for detection of the T790M mutation in plasma of NSCLC patients. This dPCR approach must replace or be used in addition to the Cobas® assay to increase the number of patients who will benefit from osimertinib.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
M.G. Denis.
Funding
Has not received any funding.
Disclosure
D. Henaff: Full/Part-time employment: ID-Solutions. L. Grewis: Officer/Board of Directors: ID-Solutions. All other authors have declared no conflicts of interest.