Abstract
489 Background: This collaborative Russian Society of Clinical Oncology (RUSSCO) and Russian Society of Pathology (RSP) study assess the extent of concordance between three validated, commercially available PD-L1 IHC assays for UC patients. Methods: Tumors from 100 UC patients were stained with SP142 (Ventana), 22C3 (Dako) and SP263 (Ventana) clones as used in the clinical trials of second-line therapy of atezolizumab, pembrolizumab and durvalumab. Four trained pathologists independently evaluated the percentages of tumor (TC) and tumor infiltrating immune cells (IC) staining positive at any intensity. One test-specific cutoff rule for each assay in this analysis was pre-specified as: IC ≥5% for SP142, TC+IC ≥10% or TC ≥10% for 22C3, and TC ≥25% or IC ≥25% for SP263. Results: 300 IHC slides were scored. Patients were predominantly male (89%) with T1 (45%) and T2 (45%) stages, respectively. The percent of IC staining across 3 assays is shown to be higher than for TC staining (45% vs. 8% for SP142; 55% vs. 24% for 22C3; 72% vs. 27% for SP263). Pearson Correlation Coefficients for IC were: 0.5, 0.69 and 0.85 between SP142/22C3, SP263/22C3 and SP142/SP263, respectively. Pearson Correlation Coefficients for TC were: 0.93, 0.99 and 0.91 for the same pairs. Table indicates the agreement analysis using recommended individual cutoffs for each test. Conclusions: If a patient with UC is classified as negative by one of the three single tests using the corresponding recommended cutoff rule, the patient will be classified as negative by any other test with a high likelihood (91%-100%), and, therefore, repeated testing can be avoided.[Table: see text]
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