Plasma cell free PD-L1 RNA expression correlated with tissue PD-L1 immunohistochemical staining and tumor mutation burden in non-small cell lung cancer.

Abstract

e15049 Background: Programmed death ligand-1 (PD-L1) protein expression by immunohistochemical staining (IHC) correlates with response to immune checkpoint inhibitor (ICI) therapies in non-small cell lung cancer (NSCLC). Tumor mutational burden (TMB) is another immune biomarker of ICI response in NSCLC. Clinical studies indicate tissue PD-L1 protein expression and TMB are independent yet complementary. Both are limited by tissue acquisition and potential heterogeneity. Plasma cell free PD-L1 RNA (cfRNA) levels and tissue protein PD-L1 expression and TMB was analyzed and correlated in patients with advanced NSCLC. Methods: Patients with advanced NSCLC underwent complementary plasma and tissue next generation sequencing (NGS) with immune biomarkers prior to treatment. Plasma PD-L1 cfRNA was assessed by the Circulogene proprietary direct-on-specimen enrichment technology NGS platform. Correlating tissue testing was performed by the Caris Molecular Intelligence platform with the anti-PD-L1 22C3 IHC antibody and TMB measuring the total number of non-synonymous somatic mutations per megabase. Results: 107 patients with advanced NSCLC were evaluated with simultaneous plasma and tissue NGS testing. 17% (95% confidence interval [CI] 10-24%) patients plasma PD-L1 positive. 48.5% (CI 38-57%) tissue IHC PD-L1 positive. 7 of 18 plasma PD-L1 positive patients were tissue PD-L1 negative. 48% (CI 39-58%) total patients TMB ≥ 10 mutations per megabase (TMB high). Correlating TMB high in 72% (CI 50-94%) of plasma PD-L1 positive and 56% (CI 42-69%) of tissue PD-L1 positive patients. TMB high in 49% (CI 37-59%) plasma PD-L1 negative and 50% (CI 35-65%) tissue PD-L1 negative patients. Conclusions: Although less frequent than tissue PD-L1 protein expression, plasma PD-L1 cfRNA expression correlated with a higher association of tissue TMB high findings than tissue PD-L1 positive patients. There was not any TMB high difference between plasma PD-L1 negative and tissue PD-L1 negative patients. Over one-third of plasma PD-L1 positive patients were tissue PD-L1 negative. Clinical correlation with immune checkpoint inhibitor therapies is ongoing.