Utility of PD‐L1 immunocytochemistry using body‐fluid cell blocks in patients with non‐small‐cell lung cancer

BACKGROUND: The expression of programmed cell death ligand-1 (PD-L1) is a biomarker in patients with non-small-cell lung carcinoma (NSCLC). Patients with advanced-stage NSCLC receive a variety of molecular genetic tests, possibly resulting in insufficient tissue for immunoassay of PD-L1. Thus, to determine whether effusion fluid specimens are a reliable alternative to tissue specimens for PD-L1 testing, we compared the results of PD-L1 immunostaining using body-fluid cell blocks and tumor tissues. METHODS: PD-L1 immunostaining was performed in 62 paired samples of cytology cell blocks (ie, immunocytochemistry) and tumor tissues (ie, immunohistochemistry) from 36 patients using the E1L3N, SP142, and SP263 anti PD-L1 antibody clones. Of the 62 cytology specimens, 50 were from malignant effusion fluid. PD-L1 expression was scored as the percentage of tumor cells with clear membranous staining. RESULTS: A strong positive correlation was observed between the immunostains on cytology cell blocks and tumor tissue (Pearson's correlation coefficient, R = .804, P /=1% and /=10% and /=50%, the overall concordance rate was 74.2% (46/62, Cohen's k = 0.568). After dichotomizing the cases using cutoff values of 1%, 10%, and 50%, the concordance rates were 84% to 100% for both adenocarcinoma and squamous cell carcinoma. The concordance rate was higher in patients with NSCLC with an EGFR mutation and using the SP263 rather than the E1L3N clone. CONCLUSION: The results of PD-L1 immunostaining of cell blocks, particularly from effusion fluid, reflect the PD-L1 expression status of NSCLC tissue.