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

A Comparative Study With Paired Surgical Specimens

Andrea Hernandez, DO; Tamar C. Brandler, MD; Fang Zhou, MD; Andre L. Moreira, MD, PhD; Nina Schatz-Siemers, DO; Aylin Simsir, MD


Am J Clin Pathol. 2019;151(4):403-415. 

In This Article

Abstract and Introduction


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.


Lung cancer remains the leading cause of cancer deaths in the United States, with non–small cell lung carcinoma (NSCLC) accounting for most cases in both men and women.[1] Patients with NSCLC often present at late stages. Chemotherapy and/or radiotherapy have historically served as first-line treatments for advanced disease but have offered limited benefit, with low response rates and low overall survival.[2,3] Immune checkpoint inhibitors targeting the programmed cell death 1 (PD-1)/programmed death–ligand 1 (PD-L1) axis have emerged as promising therapeutic agents for this group of patients.[4–6] PD-L1 immunohistochemistry (IHC) is the current predictive biomarker used to select patients for immunotherapy treatment. The efficacy of immune checkpoint inhibitors relies on the evaluation and scoring of PD-L1 expression by IHC.

To date, only patients with surgical pathology material have been included in clinical trials for PD-L1 immunotherapy. As a result, PD-L1 assays have been approved for testing on histologic specimens, with exclusion of cytologic material. However, approximately 70% of patients with lung cancer present at an advanced stage; therefore, cytology specimens may represent the initial or only material available for diagnosis and ancillary testing, often due to unresectable disease.[7,8] It is precisely these patients who may receive the most benefit from immunotherapy.

The most recent National Comprehensive Cancer Network guidelines recommend that all patients with NSCLC be tested for PD-L1 expression.[9] Over the past year, our laboratory has received increased requests for PD-L1 IHC evaluation on cytology specimens of patients with NSCLC. As a result, we performed an in-house validation and an investigational study to assess whether cytology specimens from patients with NSCLC are adequate and reliable for PD-L1 IHC evaluation. Furthermore, we compared PD-L1 scoring between paired surgical and cytologic specimens, as limited studies have investigated the level of concordance between surgical and cytologic PD-L1 scores.