Prognostic impact of <scp>PD</scp>‐<scp>L1</scp> expression in surgically resected <scp><i>EGFR</i></scp>‐mutant lung adenocarcinoma: A real‐world database study in Japan (<scp>CReGYT</scp>‐01 <scp>EGFR</scp> study)

The expression of programmed cell death-ligand 1 (PD-L1) and mutation in epidermal growth factor receptor (EGFR) are biomarkers used for perioperative treatment of lung adenocarcinoma. However, the clinical significance of PD-L1 expression in surgically resected EGFR-mutant lung adenocarcinoma remains unclear. We conducted a real-world database of patients with surgically resected lung adenocarcinoma from 2015 to 2018 was constructed across 21 centers in Japan. The association among PD-L1 expression, EGFR mutations, and prognosis was evaluated. Among 847 patients, PD-L1 expression was negative (tumor proportion score [TPS] < 1%) in 429 (51%), weakly positive (TPS = 1%-49%) in 275 (32%), and strongly positive (TPS ≥50%) in 143 (17%) patients. EGFR mutations were detected in 331 (39%) patients. PD-L1 expression was associated with poor recurrence-free survival (RFS) (p < .001) in both EGFR-mutant and wild-type patients. However, in EGFR-mutant patients, PD-L1 expression was not associated with overall survival (OS) (p = .506). Multivariable analysis confirmed an association between PD-L1 expression and RFS but not OS. Furthermore, in EGFR-mutant patients treated with EGFR-tyrosine kinase inhibitor (EGFR-TKI) treatment post-relapse, PD-L1 expression was not associated with overall response rate (p = .714), disease control rate (p = .554), or progression-free survival (p = .660). In conclusion, PD-L1 expression predicted poor RFS-independent EGFR status but did not show any association with OS in EGFR-mutant patients. The efficacy of post-relapse EGFR-TKI treatment was independent of PD-L1 expression. The significance of PD-L1 expression in perioperative EGFR-TKI therapy should be evaluated.