Introduction of programmed death-ligand 1 (PD-L1) inhibitors has significantly changed the treatment landscape of non-small-cell lung carcinomas (NSCLC). Since endobronchial ultrasound guided fine-needle aspiration (EBUS FNA) has become the primary diagnostic and staging modality for NSCLC, this study was pursued to determine the adequacy of Ventana SP263 PD-L1 assay in cytology cell blocks.
Fifty NSCLC cases with cytology and corresponding histology specimens obtained between 2014 and 2018 were identified. After assessing for adequacy (100 or more tumor cells), forty cases were selected for Ventana SP263 PD-L1 immunohistochemistry (IHC) assay and assessed for tumor proportion scores (TPS) and staining intensity scores (SIS) and analyzed for concordance.
Of the 40 matched pairs 33 (82.5%) showed concordant PD-L1 expression. On cytology, 32 cases were positive (8 high-expressors and 24 low-expressors) of which 27 were concordant and 5 discordant with matched histology specimens. On histology, 29 cases were positive (7 high-expressor and 22 low-expressors) while 11 cases were negative for PD-L1 expression of which 6 had concordant negative cytology. The intraclass correlation coefficients (ICC) for TPS was 0.81 with 95% confidence interval (0.68, 0.9) and for the SIS, it was 0.78 with 95% CI (0.62, 0.88), both considered as having excellent agreement.
With an overall concordance rate of 82.5% between cytology and histology specimen, this study demonstrates the feasibility of PD-L1 IHC with SP263 clone on cytology samples of NSCLC and adds to a growing body of evidence validating the use of cytology cell blocks for PD-L1 expression testing.

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