MA08.10 Detection of the T790M Mutation of EGFR in Plasma of Advanced NSCLC Patients with Acquired Resistance to EGFR-TKI (WJOG8014LTR)

Abstract

NSCLC patients with activating mutations of the EGFR initially respond well to TKIs, but about half such patients develop TKI resistance through acquisition of a secondary T790M mutation. Whereas next-generation EGFR-TKIs have been developed to overcome T790M-mediated resistance, performance of a second tumor biopsy to assess T790M mutation status can be problematic. We developed and evaluated liquid biopsy assays for detection of TKI-sensitizing and T790M mutations of EGFR by droplet digital PCR (ddPCR) in EGFR mutation–positive patients with acquired EGFR-TKI resistance. A total of 260 patients was enrolled between November 2014 and March 2015 at 29 centers for this West Japan Oncology Group (WJOG 8014LTR) study. Plasma specimens from all subjects as well as tumor tissue or malignant pleural effusion or ascites from 41 patients were collected after the development of EGFR-TKI resistance. All plasma samples were genotyped successfully and the results were reported to physicians within 14 days. TKI-sensitizing and T790M mutations were detected in plasma of 120 (46.2%) and 75 (28.8%) patients, respectively. T790M was detected in 56.7% of patients with plasma positive for TKI-sensitizing mutations. For the 41 patients with paired samples obtained after acquisition of EGFR-TKI resistance, the concordance for mutation detection by ddPCR in plasma compared with tumor tissue or malignant fluid specimens was 78.0% for TKI-sensitizing mutations and 65.9% for T790M. Noninvasive genotyping by ddPCR with cell-free DNA extracted from plasma is a promising approach to the detection of gene mutations during targeted treatment.