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Abstract 4037: Analytical and inter-observer comparability of 4 clinically developed programmed death-ligand 1 (PD-L1) immunohistochemistry assays in advanced clear cell renal cell carcinoma (CCRCC)

Background: PD-L1/programmed cell death-1 (PD-1)-targeting checkpoint inhibitors have shown clinical activity in advanced and metastatic RCC, which correlates with PD-L1 expression on tumor cells (TC) and/or tumor-infiltrating immune cells (IC). We examined the analytical performance and inter-observer agreement of 4 clinically developed assays for PD-L1 expression on IC and TC in locally advanced CCRCC. Methods: Archived formalin-fixed paraffin-embedded nephrectomy specimens from 30 patients with locally advanced (T2a+) CCRCC were selected from 201 cases based on PD-L1 status per VENTANA SP142 (IC 5%; 10 cases each). All selected cases were stained for PD-L1 using VENTANA SP142 and SP263, and DAKO 22C3 and 28-8, each at one site, according to manufacturer protocols. Stainings were blinded with respect to both assay and sample information and scored at 5 sites for PD-L1 expression on IC (% per tumor area) and TC (% of tumor cells). All readers had been trained in scoring IC per tumor area. Results: Adjusted means of IC staining for PD-L1 varied from 4.00 to 4.90%, and TC from 1.32 to 10.68%, depending on the assay used (Table). Pairwise comparisons of adjusted means between assays revealed small, non-significant differences for IC (-0.9 to 0.3%), while for TC there were significant differences for SP142 v other assays (-9.4 to -5.7%) and for SP263 v 28-8 (-3.7%), and small, non-significant differences for other comparisons (-2.9 to -0.8%). The pre-specified allocation to binary cutoffs (1% or 5%) for IC or TC alone predominantly showed moderate-to-substantial Kappa agreement scores (0.4 to 0.8) for IC and TC between assays for each reader. Conclusions: This is the first multicenter analytical comparison study of PD-L1 assays in CCRCC. Good-to-high concordance rates across all assays were achieved between trained readers for scoring PD-L1 on IC and for some assays for PD-L1 on TC. Citation Format: Ulrich Sommer, Markus Eckstein, Johannes Ammann, Till Braunschweig, Stephan Macher-Goeppinger, Kristina Schwamborn, Stefanie Hieke-Schulz, Bernd Wullich, Manfred Wirth, Wilfried Roth, Ruth Knuchel, Wilko Weichert, Gustavo Baretton, Arndt Hartmann. Analytical and inter-observer comparability of 4 clinically developed programmed death-ligand 1 (PD-L1) immunohistochemistry assays in advanced clear cell renal cell carcinoma (CCRCC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4037.