Abstract B073: PD-L1 expression in urothelial cancer: first results from RUSSCO-RSP assay comparision study

Abstract

Abstract Background: To compare similarities and differences between PD-L1 IHC assays in patients with urothelial cancer (UC), collaborative Russian Society of Clinical Oncology (RUSSCO) and Russian Society of Pathology (RSP) study was conducted. The first results, presented here, describe a rate of PD-L1 IHC expression assessed by each test and evaluate concordance between 3 assays. Methods: 100 UC tumors were stained with PD-L1 IHC assays (clones SP142, 22C3 and SP263) as used in the clinical trials of second-line therapy of atezolizumab (Ventana SP142), pembrolizumab (Dako 22C3), and durvalumab (Ventana SP263). Four trained pathologists certified by Ventana/Roche and Dako/Agilent in interpreting respective assays independently evaluated the percentages of tumor (TC) and tumor-infiltrating immune cells (IC) staining positive at any intensity. Single clinical cut-off for inclusion in this comparative analysis was used: IC ≥5% for SP142, TC+IC/TC ≥10% for 22C3, and TC or IC ≥25% for SP263. Results: Patients were predominantly male (89%), 47/100 (47%) had grade 3 tumors, 45/100 (45%) and 45/100 (45%) had T1 and T2 stages, respectively. 300 IHC slides were scored. The percent of immune cell staining across 3 assays appears to be higher than for tumor cell staining (45% vs. 8% for SP142; 55% vs. 24% for 22C3; 72% vs. 27% for SP263). There were variabilities in immune cell staining for all assays and in tumor cell staining across SP142 and other assays. The percentage of PD-L1-positive patients was comparable with SP142 (9%), 22C3 (11%) and SP263 (7%). Table indicates the number of cases that were concordant with the index assay scoring algorithm, when an alternative cut-off was used to determine the allocation of cases to clinical groups above and below the cut point. Table Assay clone used for slide stainingScoring AlgorithmSP142IC ≥5%22C3TC+IC / TC ≥10%SP263TC or IC ≥25%SP142100/100 (100%)92/100 (92%)95/100 (95%)22C395/100 (95%)100/100 (100%)95/100 (95%)SP26396/100 (96%)95/100 (95%)100/100 (100%) Conclusions: First comparison showed that concordance was more than 90% between SP142, 22C3, and SP263 assays used for evaluation of PD-L1 expression in patients with urothelial carcinoma. Further analysis is required to draw a final conclusion. Citation Format: Larisa Zavalishina, Patritsiya Povilaitite, Yulia Andreeva, A. Petrov, Inna Pugach, Ekaterina Kharitonova, Alexey Rumyantsev, Grigory Raskin, Georgy Frank, Sergei Tjulandin, Ilya Tsimafeyeu. PD-L1 expression in urothelial cancer: first results from RUSSCO-RSP assay comparision study [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B073.