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.