Association of Tumor PD-L1 Expression with the T790M Mutation and Progression-Free Survival in Patients with EGFR-Mutant Non-Small Cell Lung Cancer Receiving EGFR-TKI Therapy

Background: Among patients with non-small cell lung cancer (NSCLC), we compared the progression-free survival (PFS) and proportion of acquisition of T790M mutation of the epidermal growth receptor gene (EGFR) after first-line treatment with epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) in patient groups with and without tumor expression of programmed death ligand-1 (PD-L1). Methods: Data of patients with EGFR-mutant NSCLC were retrospectively analyzed. Tumor PD-L1 expression was evaluated by immunohistochemistry using the 22C3 antibody. T790M gene mutation was evaluated by Cobas EGFR assay using tissues or humoral specimens. Results: Data of 47 patients with EGFR-mutant NSCLC were analyzed. The median (95% confidence interval) PFS in the PD-L1-negative and -positive patient groups were 12.9 (9.7–15.4) months and 9.0 (5.1–12.3) months, respectively (p = 0.029). T790M gene mutation was analyzed in 27 patients. The proportion of acquisition of T790M mutation of EGFR after first-line treatment with an EGFR-TKI was higher in the PD-L1-negative patient group than in the PD-L1-positive patient group (8/11 patients (72.7%) vs. 4/16 patients (25.0%); p = 0.022). Conclusions: Patients with negative tumor PD-L1 expression showed longer PFS and a higher proportion of acquisition of T790M mutation of EGFR after first-line treatment with an EGFR-TKI.