Analytical Validation and Clinical Utility of an Immunohistochemical Programmed Death Ligand-1 Diagnostic Assay and Combined Tumor and Immune Cell Scoring Algorithm for Durvalumab in Urothelial Carcinoma

Context.-Clinical responses to anti-programmed death receptor-1 and anti-programmed death ligand-1 (PD-L1) agents are generally improved in patients with high PD-L1 expression compared with those with low/negative expression across several tumor types, including urothelial carcinoma. Objective.-To validate a PD-L1 immunohistochemical diagnostic test in urothelial carcinoma patients treated with the anti-PD-L1 monoclonal antibody durvalumab. Design.-The Ventana PD-L1 (SP263) assay was validated for intended use in urothelial carcinoma formalin-fixed, paraffin-embedded samples in studies addressing sensitivity, specificity, robustness, and precision, and implemented in study CD-ON-MEDI4736-1108 (NCT01693562). Efficacy was analyzed in patients classified according to prespecified PD-L1 expression cutoffs: PD-L1-high (if >1% of the tumor area contained tumor-associated immune cells, >= 25% of tumor cells or >= 25% of immune cells stained for PD-L1; if <= 1% of the tumor area contained immune cells, >= 25% of tumor cells or 100% of immune cells stained for PD-L1) and PD-L1-low/negative (did not meet criteria for PD-L1-high). Results.-The assaymet all predefined acceptance criteria for sensitivity, specificity, and precision. Interreader and intrareader precision overall agreement were 93.0% and 92.4%, respectively. For intraday reproducibility and interday precision, overall agreement was 99.2% and 100%, respectively. Interlaboratory overall agreement was 92.6%. In study CD-ON-MEDI4736-1108, durvalumab demonstrated clinical activity and durable responses in both PD-L1-high and PD-L1-low/negative subgroups, although objective response rates tended to be higher in the PD-L1-high subgroup than in the PD-L1-low/negative subgroup. Conclusions.-Determination of PD-L1 expression in urothelial carcinoma patients using the Ventana PD-L1 (SP263) assay was precise, highly reproducible, and clinically relevant.