Abstract
PD-L1 expression assessed by immunohistochemical staining is used for the selection of immunotherapy in non-small cell lung cancer (NSCLC). Appropriate validation of PD-L1 expression in cytology specimens is important as cytology is often the only diagnostic material in NSCLC. In a previous study comprising two different cohorts of paired biopsies and cytological specimens, we found a fairly good cyto-histological correlation of PD-L1 expression in one, whereas only a moderate correlation was found in the other cohort. Therefore, that cohort with additional new cases was now further investigated for the impact of preanalytical factors on PD-L1 concordance in paired biopsies and cytological specimens. A total of 100 formalin-fixed paraffin-embedded cell blocks from 19 pleural effusions (PE), 17 bronchial brushes (BB), and 64 bronchoalveolar lavage (BAL) and concurrent matched biopsies from 80 bronchial biopsies and 20 transthoracic core biopsies from NSCLC patients were stained using the PD-L1 28-8 assay. Using the cutoffs ≥1%, ≥5%, ≥10%, and ≥50% positive tumour cells, the overall agreement between histology and cytology was 77–85% (κ 0.51–0.70) depending on the applied cutoff value. The concordance was better for BALs (κ 0.53–0.81) and BBs (κ 0.55–0.85) than for PEs (κ −0.16–0.48), while no difference was seen for different types of biopsies or histological tumour type. A high number of tumour cells (>500) in biopsies was associated with better concordance at the ≥50% cutoff. In conclusion, the study results suggest that PEs may be less suitable for evaluation of PD-L1 due to limited cyto-histological concordance, while a high amount of tumour cells in biopsies may be favourable when regarding cyto-histological PD-L1 concordance.
Highlights
Immune checkpoint inhibitors (ICIs) are potent anticancer drugs used in a variety of malignancies including non-small cell lung cancer (NSCLC) [1,2,3,4]
Adenocarcinomas tended to be positive for programmed death-ligand 1 (PD-L1) more often than squamous cell carcinomas, regardless of specimen type, but this was only significant at cut-off ≥1% for cytological specimens (Fisher’s exact test, p = 0.012)
For histological specimens, samples with a higher tumour cell content were less often PD-L1 positive, but this was only significant for cut-off ≥5% (Pearson’s Chi-square test, p = 0.045)
Summary
Immune checkpoint inhibitors (ICIs) are potent anticancer drugs used in a variety of malignancies including non-small cell lung cancer (NSCLC) [1,2,3,4]. Immunohistochemical (IHC) staining for programmed death-ligand 1 (PD-L1) on formalin-fixed paraffinembedded (FFPE) tissue specimens has been shown to predict clinical response to programmed death-1 (PD-1)/PD-L1 immune checkpoint therapies in NSCLC [3,5,6,7,8,9,10,11,12]; PD-L1 expression in FFPE tissue is used for selecting patients for immunotherapy. PD-L1 expression in paired histological and cytological materials from NSCLC patients has been compared in several studies [19,20]. The overall agreement of PD-L1 reactivity has been reported to be relatively good between histology and cytology but with substantial variation between studies, both for concordance and proportion of positive PD-L1 NSCLC in cytological specimens
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