The detection of PD‐L1 expression on liquid‐based cytology in pleural effusion of lung adenocarcinoma and its prognostic evaluation: Between paired liquid‐based cytology and cell block samples

Abstract

BackgroundProgrammed death‐ligand 1 (PD‐L1) expression levels measured by immunohistochemistry have been proven to predict the outcome of immunotherapy in lung adenocarcinoma (LUAD). However, data on PD‐L1 expression on liquid‐based cytology (LBC) in malignant pleural effusion (MPE) is scarce.MethodsThis study cohort included 60 cases with MPE suffering from LUAD. PD‐L1 SP263 assay was used for immunocytochemistry (ICC) on LBC and matched cell block (CB) to validate ICC protocols on LBC slides. Clinical outcomes were analyzed based on immunotherapy and PD‐L1 tumor proportion scores (TPS) on LBC slides and CBs.ResultsPD‐L1 expression with TPS ≥1% was lower in LBCs than in CBs (33 of 60 [55.0%] vs. 35 of 60 [58.3%]; p = .687). Even with the TPS ≥50% threshold, PD‐L1 expression was lower in LBCs (10 of 60 [16.7%] vs. 15 of 60 [25%]; p = .125). Epidermal growth factor receptor (EGFR) exon 20 mutation, tumor cell proportion, and pleural fluid neutrophil‐to‐lymphocyte ratio were related to PD‐L1 expression on CBs (p = .013, p = 0.022, and p = .011), respectively. Patients with subsequent immune checkpoint inhibitor therapy remained a better prognostic in subgroups of PD‐L1 positive expression on LBC slides (TPS ≥1%, p = .041).ConclusionsLBC specimens had comparable performance to CBs in PD‐L1 assessment and predicting treatment response to PD‐L1‐defined therapy.