Positive PD-L1 Expression Is Associated with Unfavorable Clinical Outcome in EGFR-Mutated Lung Adenocarcinomas Treated with EGFR-TKIs

Programmed death ligand 1 (PD-L1) expression has been associated with clinical outcome of programmed death 1 (PD-1) pathway blockade in non-small cell lung cancer (NSCLC). PD-L1 is highly expressed in approximately 30% of patients without EGFR mutation or ALK rearrangement in previous trials. The objective of this study was to determine the frequency of PD-L1 expression and the clinical outcome according to PD-L1 expression in lung adenocarcinomas harboring EGFR mutation and treated with tyrosine kinase inhibitors (TKIs). We retrospectively evaluated PD-L1 expression using 22C3 pharmDx assay in lung adenocarcinoma patients with EGFR mutations at two referral hospitals between January 2017 and June 2018. Samples were obtained from surgically resected tumors, small biopsy, or cytologic cell blocks. Of all 71 patients analyzed, 44 (58.7%) had PD-L1 tumor proportion score (TPS) of