Retrospective Molecular Epidemiology Study of PD-L1 Expression in Patients with EGFR-Mutant Non-small Cell Lung Cancer

PURPOSE: Data are limited on programmed death ligand 1 (PD-L1) expression in epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: We retrospectively evaluated the relationship between PD-L1 expression and recurrence-free survival (RFS) and overall survival in 319 patients with EGFR-mutant NSCLC who were treated at Samsung Medical Center from 2006 to 2014. Membranous PD-L1 expression on tumor cells was measured using the PD-L1 IHC 22C3 pharmDx antibody and reported as tumor proportion score (TPS). Kaplan-Meier methods, log-rank test, and Cox proportional hazards models were used for survival analysis. RESULTS: All patients had ≥1 EGFR mutation—54% in exon 19 and 39% in exon 21. Overall, 51% of patients had PD-L1–positive tumors. The prevalence of PD-L1 positivity was higher among patients with stages II-IV versus stage I disease (64% vs. 44%) and among patients with other EGFR mutations (75%) than with L858R mutation (39%) or exon 19 deletion (52%). PD-L1 positivity was associated with shorter RFS, with an adjusted hazard ratio of 1.52 (95% confidence interval [CI], 0.81 to 2.84; median, 18 months) for the PD-L1 TPS ≥ 50% group, 1.51 (95% CI, 1.02 to 2.21; median, 31 months) for the PD-L1 TPS 1%-49% group, and 1.51 (95% CI, 1.05 to 2.18) for the combined PD-L1–positive groups (TPS ≥ 1%) compared with the PD-L1–negative group (median, 35 months). CONCLUSION: PD-L1 expression is associated with disease stage and type of EGFR mutation. PD-L1 positivity might be associated with worse RFS among patients with surgically treated EGFR-mutant NSCLC.