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

Abstract

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. 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. A strong positive correlation was observed between the immunostains on cytology cell blocks and tumor tissue (Pearson's correlation coefficient, R = .804, P < .001). When the score was categorized as <1%, ≥1% and <10%, ≥10% and <50%, 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. The results of PD-L1 immunostaining of cell blocks, particularly from effusion fluid, reflect the PD-L1 expression status of NSCLC tissue.