Programmed death ligand 1 testing in non–small cell lung carcinoma cytology cell block and aspirate smear preparations

BACKGROUND: Immune checkpoint inhibitors targeting the programmed cell death 1 (PD-1) receptor and its ligand, programmed death ligand 1 (PD-L1), have emerged as a therapeutic approach for patients with non–small cell lung carcinoma (NSCLC). PD-L1 expression, assessed by immunohistochemistry (IHC), is used to select patients for PD-1/PD-L1 inhibitor therapy. Most studies have been performed with histology specimens, with limited data available on the performance in cytology specimens. This study evaluated PD-L1 in cytology specimens and compared the results with those from paired core-needle biopsy for concordance. METHODS: Forty-one NSCLC fine-needle aspiration cases that had paired core-needle biopsy specimens with PD-L1 IHC were selected. A Papanicolaou-stained direct smear and a cell block section from each case were stained with a Dako PD-L1 pharmDx antibody (clone 22C3). Only slides with 100 or more tumor cells (37 smears and 38 cell blocks) were evaluated. Tumor proportion scores (TPS) were assessed on the basis of the partial/complete membranous staining of tumor cells and were correlated with those of paired core-needle biopsy. RESULTS: All 9 smears that were negative for PD-L1 staining showed 100% concordance with the paired core-needle biopsy, whereas 28 smears with PD-L1 expression showed a similar TPS, except for 1 smear that was discordant. In contrast, 10 negative paired core-needle biopsy cases corresponded to 9 concordant negative cell blocks, whereas 1 cell block had a TPS of 1% to 5%. The remaining 28 cell blocks demonstrated PD-L1 expression, with 22 cases showing a TPS similar to that of the paired core-needle biopsy, whereas 6 cell blocks were discordant, likely because of intratumoral heterogeneity. CONCLUSIONS: The results show that NSCLC cytology samples evaluated for PD-L1 have high concordance with paired core-needle biopsy samples and can be used for assessing PD-L1 expression. Cancer Cytopathol 2018;126:342-52.