MA15.07 Different Responses to Osimertinib in Primary and Acquired EGFR T790M-Mutant NSCLC Patients

Abstract

Primary EGFR T790M could be occasionally identified by routine molecular testing in tyrosine kinase inhibitor TKI-naive non-small cell lung cancer (NSCLC) patients. This study was aimed to compare clinical characteristics of primary and acquired T790M mutations and their responses to Osimertinib in NSCLC patients. We collected clinical characteristics of patients diagnosed with epidermal growth factor receptor (EGFR) mutation from 2012 to 2017 in Shanghai Chest Hospital. For patients with primary and acquired T790M mutations, the responses to Osimertinib were analyzed. Primary T790M was identified in 1.03% (61/5900) of TKI-naive patients. Acquired T790M was detected in 45.50% (96/211) of TKI-treated patients. T790M always coexisted with sensitizing EGFR mutations. Primary T790M was always coexisted with 21L858R (45/61) whereas acquired T790M was coexisted with 19del (61/96). Among them, 18 patients with primary T790M mutation acquired Osimertinib and 75 patients with acquired T790M mutation received Osimertinib. The median progression-free survival (mPFS) of Osimertinib in primary T790M group was greatly longer than that in acquired T790M group (18.0 months:95% CI:15.0-21.0 VS 10.0months:95% CI:8.3-11.7, P=0.016). The DCR of both groups were 89.3% and 100%. In primary T790M group, the mPFS of concomitant occurrence of 20 T790M and 21 L858R or 19del were 15.7m and 24.0 m, respectively. In acquired T790M group, the mPFS of concomitant occurrence of 20 T790M and 21 L858R or 19del were 11.0m and 10.0m, respectively. Primary and acquired T790M-mutation patients showed different molecular characteristics. Both of them may respond to Osimertinib. However, primary T790M patients showed greater survival benefits from Osimertinib than acquired T790M patients.