ctDNA detection of EGFR mutations in NSCLC patients using TargetSelector.
e23037 Background: EGFR mutations are the most frequent targetable genomic alterations in non-small cell lung cancer (NSCLC) patients (pts). While tissue biopsy remains the standard for assessing of EGFR mutation status, it is invasive and not always feasible. Liquid biopsy is a minimally invasive alternative. Biocept’s proprietary TargetSelector system evaluates circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in blood. We aimed to clinically validate the accuracy of EGFR-specific TargetSelector in NSCLC pts. Methods: At three time points (T0: baseline before TKI, T1: during EGFR-TKI therapy, T2: after progression), blood samples were collected in Biocept OncoCEE BCT validated to preserve DNA up to 8 days. These samples were interrogated for three EGFR mutations: exon 19 deletions (Del 19), L858R, and T790M. The objectives are to assess detection sensitivity of liquid biopsy using EGFR mutation status vs the tissue as gold standard and to evaluate whether the detection sensitivity changes with EGFR-TKI therapy. Results: A total of 53 study pts were enrolled (male, 21; female, 32). The mean age was 70.6 (range: 46 – 90). Most pts had stage IV disease (43, 81.1%) and lung adenocarcinoma (48, 90.6%). 26 (49.1%) pts had EGFR mutations in tumor tissue: Del 19, 13; L858R, 8; T790M, 6; other, 8. Detection sensitivity for sensitizing EGFR mutations (Del 19 and L858R) at T0, T1, and T2 was 60.0% (6/10), 33.3% (5/15), and 33.3% (1/3), respectively. There was no statistical difference in CTC counts between activating EGFR mutation-positive and -negative pts (mean CTC count: 10.5 vs 20.1; p = 0.11 by two-sided t-test). Detection sensitivity for T790M was 33.3% (2/6) and 5 of 6 pts were receiving T790M directed therapy (3, rociletinib; 2, osimertinib) at the time of blood draw. Two pts – one patient before initiation of EGFR-TKI and the other during treatment with erlotinib – were found to have T790M mutations only in blood and not in tissue. Conclusions: Activating EGFR mutation detection may decrease during the course of TKI therapy, possibly due to treatment response. Further research with an expanded sample size and serial collections are needed to evaluate this finding, and to investigate possible implications of the presence of T790M only in blood.