PD-L1 expression and response to pembrolizumab in patients with EGFR-mutant non-small cell lung cancer

Epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer is less likely to express programmed death-ligand 1 (PD-L1) than tumors with wild-type EGFR and is associated with poor response to pembrolizumab. To understand the relationship between EGFR mutation and PD-L1 expression in pembrolizumab response, we retrospectively evaluated the factors contributing to the high tumor proportion score in 155 EGFR-mutant non-small cell lung cancer cases and their associated response to pembrolizumab. Uncommon EGFR mutations were significantly associated with a PD-L1 tumor proportion score ≥ 50% compared to common EGFR mutations. The objective response rate to pembrolizumab of 14 patients was 36%, including 22% in patients with common EGFR mutations, 60% in patients with uncommon EGFR mutations and 75% in patients with both uncommon mutations and a PD-L1 tumor proportion score ≥ 50%. A PD-L1 tumor proportion score ≥ 50% was more frequent in non-small cell lung cancer patients harboring uncommon EGFR mutations and was associated with pembrolizumab efficacy.