Significance of PD-L1 expression in the cytological samples of non-small cell lung cancer patients treated with immune checkpoint inhibitors

Objectives: The programmed death-ligand 1 (PD-L1) tumor proportion score (TPS) in tumor tissue samples is an established clinical biomarker for non-small cell lung cancer (NSCLC). However, the significance of PD-L1 expression in other types of samples has not been fully investigated. Patients and methods: We conducted a multicenter retrospective cohort study of advanced NSCLC patients who received ICI treatment during the clinical course and investigated the effects of ICIs according to PD-L1 expression in cytology samples, including cell block and endobronchial ultrasound-guided (EBUS) transbronchial needle aspiration (TBNA) samples. Results: A total of 264 patients were included in this study: PD-L1 expression was determined in cell block or TBNA specimens in 55 patients, and in tissue samples in 209 patients. Among the former patients, the median progression-free survival (PFS) of those with a TPS for PD-L1 ≥ 50% was significantly longer compared to that of those with a TPS < 50% (6.5 vs. 1.9 months, respectively, p = 0.008). When the cutoff value was set at 1%, the median PFS was 4.2 months in patients with a TPS ≥ 1% and 1.5 months in patients with a TPS < 1% (p < 0.001). Conclusion: PD-L1 expression determined using cytology specimens predicts the efficacy of ICIs.