PD-L1 expression in malignant pleural effusion samples and its correlation with oncogene mutations in non-small cell lung cancer

BACKGROUND: Programmed death ligand 1 (PD-L1) tumor proportion score (TPS) is currently widely used for selection of immune therapies in non-small cell lung cancer (NSCLC). Most of samples for PD-L1 expression were obtained from tumor tissue. However, the feasible of malignant pleural effusion (MPE) cytological samples for PD-L1 detection is poorly reported. And the correlation between oncogene mutations and PD-L1 expression based on high-throughput sequencing is rarely studied. METHODS: NSCLC MPE cytological samples and partially paired tumor tissue from our institution analyzed for PD-L1 immunohistochemistry (IHC) using the clone SP263 pharmDx kit and evaluated genomic aberrations in all patients using next generation sequencing (NGS). RESULTS: One hundred and twenty-three MPE cell blocks and 29 paired tumor tissue were successfully tested for PD-L1 expression. PD-L1 TPS of ≥50% were seen in 18.7% (23/123) of all samples. The accordance of PD-L1 expression in tumor tissue and MPE samples was 86.2% (50% as cut-off value). PD-L1 TPS ≥50% tumors were significantly associated with EGFR wild-type (P=0.007), but, no correlation between other genes and PD-L1 expression. A trend of longer overall survival (OS) was observed in patients with PD-L1 TPS <50% than those TPS ≥50% (20.0 vs. 13.8 months, P=0.057). No difference of tumor mutational burden (TMB) was observed between patients with PD-L1 ≥50% and <50% (8.2/MB and 7.7/MB, P=0.47). CONCLUSIONS: Our results suggest that cytological material is feasible for PD-L1 IHC analysis. Gene alterations could partially contribute to select the samples that with different PD-L1 expression. No correlation between the PD-L1 expression and TMB.