Comparative evaluation of PD-L1 expression in cytology imprints, circulating tumor cells and tumor tissue in non-small cell lung cancer patients.

Alternative sources of tumor information need to be explored in patients with non-small cell lung cancer (NSCLC). Here, we compared programmed cell death 1 ligand 1 (PD-L1) expression on cytology imprints and circulating tumor cells (CTCs) with PD-L1 tumor proportion score (TPS) from immunohistochemistry staining of tumor tissue from patients with NSCLC. We evaluated PD-L1 expression using a PD-L1 antibody (28-8) in representative cytology imprints, and tissue samples from the same tumor. We report agreement rates on PD-L1 positivity (TPS ≥ 1%) and high PD-L1 expression (TPS ≥ 50%). Considering high PD-L1 expression, cytology imprints showed a PPV of 64% and a NPV of 85%. CTCs were detected in 40% of the patients and 80% of them were PD-L1+ . Seven patients with PD-L1 expression of <1% in tissue samples or cytology imprints had PD-L1+ CTCs. The addition of PD-L1 expression in CTCs to cytology imprints markedly improved the prediction capacity for PD-L1 positivity. The combined analysis of cytological imprints and CTCs provides information on the tumoral PD-L1 status in NSCLC patients, which might be used when no tissue is available.