Impact of tumor microenvironment on the efficacy of epidermal growth factor receptor-tyrosine kinase inhibitors in patients with EGFR-mutant non-small cell lung cancer

We retrospectively investigated the impact of the tumor microenvironment (TME) on the efficacy of epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) as first-line treatment in 70 patients with advanced EGFR-mutant non-small cell lung cancer and who were seen at Osaka City University Hospital (Osaka, Japan) between August 2013 and December 2017. Using immunohistochemical staining with 28-8 and D7U8C Abs, the tumor proportion score was assessed for programmed cell death-1 ligand-1 (PD-L1), as high (50% or more) or low (less than 50%), and ligand-2 (PD-L2) expression, respectively. The extent of CD8(+) tumor-infiltrating lymphocytes was evaluated on a scale of 0-3, with 0-1 as low and 2-3 as high. The TME of the 52 evaluable pretreatment specimens was categorized into 4 subtypes, according to the respective PD-L1 tumor proportion and CD8(+) scores, as follows: (a) high/high (13.5%, n = 7); (b) low/low (42.3%, n = 22); (c) high/low (17.3%, n = 9); and (d) low/high (26.9%, n = 14). Expression of PD-L2 was significantly the highest in type 1 (57.1% vs 4.5% vs 11.1% vs 7.1%, respectively; P = .0090). Response rate was significantly the lowest in type 1 (14.3% vs 81.8% vs 66.7% vs 78.6%, respectively; P = .0085). Progression-free survival was the shortest in type 1 and the longest in type 4 (median, 2.4 vs 11.3 vs 8.4 vs 17.5 months, respectively; P = .00000077). The efficacy of EGFR-TKIs differed according to the TME, and the phenotype with high PD-L1 and CD8(+) expression might be the subset that would poorly benefit from such treatment.