P3.02b-008 Quantification and Monitoring of Treatment Response in EGFR Mutant NSCLC Patients by Digital-PCR in Plasma cftDNA: Topic: EGFR Biomarkers

Abstract

The identification of activating epidermal growth factor receptor (EGFR) mutations is essential for deciding therapy of non-small cell lung cancer (NSCLC) patients. Circulating cell-free tumor DNA (cftDNA) holds promise as a non-invasive methodology for tumor monitoring in solid malignancies. Among advanced NSCLC patients with an acquired resistance to EGFR-tyrosine kinase inhibitors (TKIs), about 50% carry T790M mutation, but its frequency in EGFR-TKI-naıve patients and dynamic change during therapy remains unclear. We hypothesized that EGFRmutation analysis detection in cftDNA for NSCLC may be feasible for monitoring treatment response to EGFR-TKIs and also predict drug resistance. EGFR sensitive mutations and T790M were analyzed using digital PCR (d-PCR) (Quant studio 3D, life technologies) in longitudinally (at baseline, at 4, 8, 20, 60, 120, 180, 270, 360 days) collected plasma samples (n=50) from 8 tissue-confirmed EGFR-mutant NSCLC patients treated with an EGFR-TKI (Gefitinib N = 4; Erlotinib N = 1; Afatinib N = 3). DNA extracted from plasma of 8 healty blood donors were used to detect the specificity of EGFR mutant assay. Tumor assessment was performed according to RECIST criteria 1.1 every two months. The sensitivity of d-PCR in plasma versus tissue was 71.4%. No EGFR mutation was present in the 8 control cases (specificity of 100%). Of four patients who developed progression disease (PD), in the samples of progression, T790M was detected in 75% of cases. The frequency of T790M in pre-TKI plasma samples was of 37.5%. EGFR sensitive mutations decreased at PD while T790M mutation increased in 75% of patients. Patients with concomitant pre-TKI EGFR 19 deletion and T790M showed a PD before of 12 months compared to those with L858R. T790M was frequently detected when new lesions were developed. Four patients had T790M level decreased to undetectable level with longer PFS than those with detectable T790M in blood. Our results indicated that d-PCR was a highly sensitive and useful method for detecting the T790M mutation. Moreover, dynamically monitoring T790M change might help determining EGFR-TKI resistance. We thank Italian Association for Cancer Research (AIRC) for supporting the study.