461P - The role of plasma epidermal growth factor receptor mutations test in non-small cell lung cancer

Abstract

Background: Detecting epidermal growth factor receptor (EGFR) mutated in NSCLC patients by plasma samples (ctDNA) is a non-invasive method, which has demonstrated many substantial benefits in clinical practice. In this study, we evaluated the possibility of detecting EGFR mutations in plasma of stage IIIB-IV NSCLC patients, and monitoring the genetic changes of mutations in the course of treatment. Methods: Prospective study with longitudinal follow-up. Plasma and tissue samples of 73 stage IIIB-IV NSCLC cases, including 68 cases of newly diagnosed and 5 cases of EGFR mutation positive being underwent treatment were analyzed to define EGFR mutation status. Pyrosequencing was used for tumor tissue, and scorpions ARMS was used for plasma analysis. Response evaluation based on criteria RECIST v.1.1. Results: EGFR mutation frequency was 45.6% (31/68) in tissue samples, and 29.4% (20/68) in plasma samples. The difference was statistically significant (p = 0.026) with EGFR mutations frequency in tissue and plasma samples. Concordance rate of EGFR mutation test between ctDNA and tumor samples was 83.8% (95%CI: 72.9 - 91.6), with sensitivity was 65.4% (95%CI: 45.4 - 80.8), and specificity was 100.0% (95%CI: 90.5 - 100.0). Positive predict value and negative predict value of EGFR mutations testing with ctDNA was 100.0% (95%CI: 83.2 - 100.0) and 77.1% (95%CI: 62.7 - 88.0) respectively. Concordance rate, sensitivity and specificity of 19del mutations were 91.2%, 68.4% and 100.0% respectively; according to T790M mutation were 92.6%, 25.0% and 96.9% respectively; and according to L858R mutation were 95.6%, 70.0%, and 100.0% respectively. Secondary T790M mutation was 44.4% (4/9) cases of acquired resistance of EGFR TKIs, after a median time of about 11.9 months. Conclusions: With high concordance rate and specificity, EGFR mutation testing with ctDNA by scorpions ARMS technology will be a good choice if the tissue sample is insufficient, and demonstrates the feasibility in monitoring the acquired resistance T790M mutation. However, it is necessary to test with tissue sample to have confirmed result. Legal entity responsible for the study: Ethics Committees of Cho Ray hospital Funding: Qiagen Global for patient free testing. AstraZeneca Vietnam for publishing. Disclosure: All authors have declared no conflicts of interest.