Plasma cell-free RNA PD-L1 or tissue PD-L1 protein expression and outcomes with first-line immunotherapy in metastatic non-small cell lung cancer

Abstract

BackgroundTissue programmed death ligand-1 (PD-L1) protein expression is associated with immune checkpoint inhibitor (ICI) treatment benefit in metastatic non-small cell lung cancer (NSCLC). However, tissue PD-L1 protein testing is limited by sampling tumor heterogeneity and fraught with tissue acquisition difficulties. A liquid biopsy-based PD-L1 assay could overcome these limitations of tissue PD-L1 testing. MethodsAn observational cohort of patients with metastatic NSCLC treated with first-line ICI-based therapies were retrospectively assessed for a pre-planned endpoint of median and 3-year landmark overall survival (OS) based upon plasma cell-free RNA (cfRNA) PD-L1 expression by a commercial exosome-free real-time qPCR assay or tissue PD-L1 protein expression (Dako 22C3) performed in CLIA/CAP accredited laboratories. Results53 contemporaneous patients in 3 patient cohorts were compared with a median follow-up 34 months. 16 patients were cfRNA plasma PD-L1 positive, including 6 (37 %) tissue PD-L1 negative or tissue quantity not sufficient for testing; 16 were plasma PD-L1 negative but tissue PD-L1 positive; 21 were both plasma and tissue PD-L1 negative. OS was identical whether positive plasma cfRNA PD-L1 expression or positive tissue PD-L1 protein expression (median OS 15 months; 3-year landmark OS 30 %; hazard ratio (HR) 0.97; 95 % CI, 0.44–2.10; p-value = 0.93). Within the positive plasma PD-L1 cohort there was no differing OS whether tissue PD-L1 positive, negative, or unknown (median OS 15 months; 3-year landmark OS 30 %; HR 1.15; 95 % CI, 0.322–4.05; p-value = 0.81). Positive plasma cfRNA expression was associated with a numerically longer median and higher 3-year OS compared to patients lacking PD-L1 expression (median 15 months versus 8 months; 3-year landmark OS 30 % versus 15 %; HR 0.57, 95 % CI 0.26–1.20; p-value = 0.11). ConclusionsIn this retrospective study of real-world metastatic NSCLC patients, plasma cfRNA PD-L1 expression was similarly predictive of ICI benefit as tissue PD-L1 protein expression.