Comparison of programmed death-ligand 1 (PD-L1) immunostain for nonsmall cell lung carcinoma between paired cytological and surgical specimens

Background: programmed death-ligand 1 (PD-L1) is a ligand for the inhibitory programmed cell death protein 1 (PD-L1), which are targeted by several anti-PD-1 and PD-L1 drugs for lung cancer treatment. In clinical practice, many lung cancer cases only have cytology samples available to test PD-L1. Our current study compared the PD-L1 immunohistochemistry (IHC) between paired cytological and surgical samples. Materials and Methods: Formalin-fixed lung cancer tissue microarray and paired cell blocks and surgical specimens from the same patients with a confirmed diagnosis of lung squamous cell carcinoma (SCC, n = 29) and adenocarcinoma (AC, n = 23) were sectioned for PD-L1 IHC. Results: PD-L1 was expressed on tumor cells in 16 of 29 (55%) SCC surgical specimens and 18 of 29 (62%) paired cytologic specimens with 83% matched immunostains. PD-L1 was expressed on tumor cells in 13 of 23 (57%) AC surgical specimens and in 17 of 23 (74%) paired cytologic specimens with 79% matched immunostains. The PD-L1 was expressed on inflammatory cells in 20 of 23 (87%) AC surgical specimens and in 15 of 23 (65%) paired cytologic specimens with 70% matched immunostains. The PD-L1 was expressed on inflammatory cells in 18 of 29 (62%) SCC surgical specimens and in 12 of 29 (41%) paired cytologic specimens with 79% matched immunostains. Conclusions: PD-L1 immunostain in cytology samples matched very well with paired surgical samples in both SCC and AC cases. The cytologic samples present slightly higher sensitivity for PD-L1 immunostain on tumor cells as compared to surgical biopsies.