Impact of cytotoxic chemotherapy on PD-L1 expression in patients with non-small cell lung cancer negative for EGFR mutation and ALK fusion.

OBJECTIVES: Immune-checkpoint inhibitors (ICIs) are now an established therapeutic option for advanced non-small cell lung cancer (NSCLC). It has remained unclear, however, whether cytotoxic chemotherapy affects the immune microenvironment in NSCLC wild type for EGFR and ALK.
MATERIALS AND METHODS: We retrospectively evaluated changes in programmed cell death 1-ligand 1 (PD-L1) expression, tumor mutation burden (TMB), and CD8+ tumor-infiltrating lymphocyte (TIL) density in NSCLC patients who underwent rebiopsy at the site of recurrence after postoperative platinum-based adjuvant chemotherapy, or in those who underwent rebiopsy after one or more chemotherapeutic regimens at the advanced stage. The PD-L1 tumor proportion score (TPS) and CD8+ TIL density were determined by immunohistochemistry. TMB was estimated by next-generation sequencing with a cancer gene panel (409 genes).
RESULTS: Seventeen patients with NSCLC wild type for EGFR and ALK were enrolled. Although PD-L1 TPS tended to be increased in rebiopsy samples compared with initial biopsy tissue, this difference was not significant (P =  0.113). Seven patients showed an increase in PD-L1 TPS, with this change being pronounced in four. Two cases in which PD-L1 TPS increased from 0 to 90% or from 0 to 95% after cytotoxic chemotherapy also showed a durable response to subsequent treatment with an ICI. No substantial correlation between PD-L1 TPS and TMB was apparent either before (R = 0.112) or after (R = 0.101) chemotherapy. A moderate correlation was detected between PD-L1 TPS and CD8+ TIL density before chemotherapy (R = 0.517) and a negligible correlation after (R = 0.0219).
CONCLUSION: Cytotoxic chemotherapy may change the biological characteristics of tumors including PD-L1 expression level and TMB.