Plasma Cell-free RNA PD-L1 Compared to Tissue PD-L1 Protein Expression and Outcomes with First-line Immunotherapy in Metastatic Non-small Cell Lung Cancer

Tissue programmed death ligand-1 (PD-L1) protein is the recognized predictive immune biomarker of immune checkpoint inhibitor (ICI) treatment benefit in metastatic non-small cell lung cancer (NSCLC). However, tissue PD-L1 protein testing can be limited by tumor heterogeneity and fraught with tissue acquisition difficulties. A plasma PD-L1 assay potentially overcomes these tissue limitations. Patients with metastatic NSCLC treated with first-line ICI-based treatment and available results of plasma cfRNA PD-L1 by real-time polymerase chain reaction (RT-PCR) and tissue PD-L1 protein PD-L1 with the Dako 22C3 monoclonal antibody were retrospectively assessed for median and landmark 3-year overall survival (OS). 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). Positive plasma cfRNA PD-L1 patients also demonstrated 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 0.56; 95% CI, 0.27-1.17). Plasma cfRNA PD-L1 expression by RT-PCR was similarly predictive of ICI-based treatment benefit as tissue PD-L1 protein expression.