Assay performance of the PD-L1 IHC 28-8 pharmDx assay in squamous cell carcinoma of the head and neck (SCCHN).

Abstract

e14588 Background: The PD-L1 IHC 28-8 pharmDx assay has been developed for use in detection of PD-L1 protein in formalin-fixed, paraffin-embedded (FFPE) non-squamous NSCLC and melanoma tissues for associated treatment effect with nivolumab. Validation of the assay for measuring PD-L1 expression level in human squamous cell carcinoma of the head and neck (SCCHN) FFPE sections has been conducted and results are described. Methods: Visualization of the PD-L1 IHC 28-8 pharmDx assay is based on the EnVision FLEX IHC technology. As described in the Instructions For Use, antigen retrieval was performed using the Dako PT Link, and the automated staining was conducted with Autostainer Link 48. The assay performance was validated on commercially procured FFPE SCCHN specimens. Results: Assessment of assay sensitivity to PD-L1 expression was measured on 236 unique specimens originating from squamous cell carcinoma of the tongue, tonsil, nasopharynx, oropharynx, hypopharynx, and larynx. The study demonstrated PD-L1 positive staining across a range of 0-95% positive tumor cells and 0 to 3+ staining intensity. Among these tested specimens, 44% of specimens had PD-L1 expression levels ≥1%. Assay robustness was validated by assessing critical parameters such as target retrieval solution pH, target retrieval solution temperature, target retrieval time, and cut section thickness. Assay reproducibility was evaluated in a study at three external sites. Reproducibility of intra-site, inter-day, and inter-site agreement was assessed in addition to inter- and intra-observer agreement. Assay robustness and reproducibility demonstrated agreement estimates above 85% with values for lower bound 95% confidence intervals calculated above 85%. Conclusions: These studies demonstrate that the PD-L1 IHC 28-8 pharmDx assay is reproducible and robust when used for automated detection of PD-L1 protein in FFPE human SCCHN specimens using Autostainer Link 48.