Assessment of Programmed Death-Ligand 1 (PD-L1) Immunohistochemical Expression on Cytology Specimens in Non-Small Cell Lung Carcinoma

Abstract

Objectives: To evaluate whether non-small cell lung carcinoma (NSCLC) cytology specimens are reliable for programmed death-ligand 1 (PD-L1) immunohistochemical (IHC) testing.

Methods: Fifty-two cell blocks (CBs) with corresponding surgical pathology PD-L1 IHC testing were stained with a Dako PD-L1 pharmDX antibody (clone-22C3). Tumor cellularity was recorded as <100 or ≥100 cells. PD-L1 IHC was scored by percentage of tumor cells staining (<1%, ≥1%-49%, ≥50%) and compared between matched cases.

Results: Substantial agreement (κ = 0.63; 95% CI, 0.53-0.73) was reached between matched CB and surgical cases in CBs with ≥100 tumor cells compared to CBs with <100 tumor cells (slight agreement, κ = 0.19; 95% CI, 0.04-0.35). Overall, there was 67% agreement among paired cases (35/52 cases, κ = 0.51; 95% CI, 0.42-0.60).

Conclusions: CBs can be utilized for PD-L1 IHC testing, as illustrated by the 67% agreement between CB and surgical cases in our study. Disagreement is attributable to intratumoral heterogeneity and CB cellularity.

Keywords: Cell block; Cytology; Effusion; Fine-needle aspiration; Immunohistochemistry (IHC); Immunotherapy; Non–small cell lung carcinoma (NSCLC); Programmed death–ligand 1 (PD-L1).