Optimizing PD-L1 evaluation on cytological samples from advanced non-small-cell lung cancer.

Aim: Programmed cell death-ligand 1 (PD-L1) predicts response to immune checkpoint inhibitors in non-small-cell lung cancer (NSCLC) patients. Most NSCLCs are diagnosed at an advanced stage and using minimally invasive diagnostic procedures that yield small biopsies or cytological samples. Methods: Cytological smears and paired histological samples from 52 advanced NSCLC patients were tested for PD-L1 expression by immunocyto/histochemistry (ICC/IHC) and for PD-L1 gene status by FISH. Results: PD-L1 was overexpressed in 9/52 (17%) cytological samples and in seven (13.5%) matched biopsies. The concordance between immunocytochemistry and IHC was 92.3% (48/52; p < 0.001). The concordance between PD-L1 gene status on cytology and histology was 69.2% (18/26; p < 0.001). No correlation between IHC and fluorescence in situ hybridization results was found. Conclusion: Our data support the feasibility and reliability of PD-L1 protein and PD-L1 gene assessment on direct cytological smears from NSCLC patients whenever histological sample are inadequate.