IBCN 2018: PD-L1 Assays in Muscle-Invasive Bladder Cancer for First-Line Treatment with Atezolizumab and Pembrolizumab

Rotterdam, The Netherlands (UroToday.com) Markus Eckstein analyzed the performance and agreement of four FDA/EMA-approved PD-L1 assays to detect PD-L1 expression in tumor and immune cells in muscle-invasive bladder cancer (MIBC). 173 formalin-fixed, paraffin-embedded MIBC were analyzed on tissue microarrays with four cores (1 mm diameter) of each tumor. Stains were performed in certified laboratories on Ventana Benchmark Ultra (Ventana-assays) and Dako Link 48 (Dako-assays) autostainers.

Stains were read on an assay-by-assay basis by two trained pathologists. Overall percentage agreement (OPA) was calculated across preset cut-offs. Positive (PPA) and negative percentage agreements (NPA) were calculated across different scoring algorithms. Venn diagrams were constructed to illustrate discordance according to the recent FDA/EMA guidelines.

The Dako 28-8, 22c3 and the Ventana SP263 assays showed high inter-assay correlation (r-range 0.74-0.87). Inter-assay variability between the Ventana SP142 and the three other assays was moderate (r-range 0.47-0.67). OPA of 90.2% was achieved between the Dako and the Ventana SP263 assays at multiple cut-offs. OPA with the SP142 assay was 82.1%. Pooled PPA and NPA of different scoring algorithms was 81.3% and 97.1% for the Dako and the SP263 assays. With the SP142 assay pooled PPA reached just 43.4%. The SP142 assay identifies fewer patients as eligible for first line treatment with Atezolizumab or Pembrolizumab.

In conclusion, while the Dako and SP263 assays show comparable performance, the SP142 is an outlier which leads to a significantly reduced detection rate of eligible patients for first-line treatment with Atezolizumab and Pembrolizumab according to the new FDA/EMA restrictions.

Presented by: Markus Eckstein, Institute of Pathology, University Hospital Erlangen

Written by: Stephen B. Williams, M.D., Associate Professor, Division of Urology, The University of Texas Medical Branch, Galveston, TX. and Ashish M. Kamat, M.D. Professor, Department of Urology, Division of Surgery, The University of Texas MD Anderson Cancer Center, Houston, TX at the 16th Annual Meeting of the International Bladder Cancer Network (IBCN) October 11-13, 2018 - the Inntel Hotels Rotterdam Centre, Rotterdam, The Netherlands