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

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. Cytological smears and paired histological samples from 52 advanced NSCLC patients were tested for PD-L1 expression by immunocyto/histochemistry (ICC/IHC) and for gene status by FISH. 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 gene status on cytology and histology was 69.2% (18/26; p < 0.001). No correlation between IHC and fluorescence hybridization results was found. Our data support the feasibility and reliability of PD-L1 protein and gene assessment on direct cytological smears from NSCLC patients whenever histological sample are inadequate.