Different efficacy of osimertinib in pre-TKI treated NSCLC patients with brain metastases harboring EGFR exon 19del and L858R mutant.

e21667 Background: Previous studies suggested that the efficacy of osimertinib was better in patients with epidermal growth factor receptor ( EGFR) exon 19 deletion (ex19del) than exon 21 Leu858Arg (L858R). However, the differential clinical outcomes of osimertinib in previous tyrosine kinase inhibitors (TKIs) treated non-small-cell lung cancer (NSCLC) patients with brain metastases (BrMs) according to the two different common EGFR genotypes remains undetermined. Methods: We retrospectively collected EGFR mutant (ex19del and L858R) NSCLC patients with BrMs and received osimertinib treatment between Jan 2016 and Feb 2019 in our hospital. Other eligible standards including Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-2, osimertinib 80mg monotherapy and neurologic symptoms existing was permitted to enroll in our study. Results: 78 patients with EGFR mutant NSCLC and BrMs were included in the study. EGFR mutation types were ex19del in 55% of patients (43/78) and L858R in 45% of patients (35/78). All of patients received at least one prior EGFR-TKI therapy, among which 46% (36/78) had gefitinib, 49% (38/78) had erlotinib, 19% (15/78) had icotinib. T790M status at osimertinib initiation was positive in 81% of patients (63/78), negative in 4% (3/78), unknown in 15% (12/78). The systemic objective response rate (ORR) was 46%. There was no apparent difference in systemic ORR (49% vs 43%, P = 0.598) between ex19del group and L858R group. The median progression free survival (PFS) and overall survival (OS) were 7.0 (range 4.7-9.3) and 18.8 (range 14.0-23.5) months for all patients. The median PFS in the ex19del and L858R subgroups was 9.1 (range 6.0-12.1) months and 5.3 (range 3.4-7.2) months, respectively ( P = 0.031). The median OS in the ex19del and L858R subgroups was 26.0 (range 13.7-38.3) months and 13.9 (range 7.7-20.2) months, respectively ( P = 0.033). Multivariate analysis identified L858R and ECOG PS 2 as poor independent predictors to the PFS and OS. Conclusions: The efficacy of osimertinib was associated with EGFR genotypes in pre-TKI treated NSCLC patients with BrMs, and L858R maybe an independent bad factor for long-term outcomes of osimertinib.