Concordance between four PD-L1 immunohistochemical assays and 22C3 pharmDx assay in esophageal squamous cell carcinoma in a multicenter study

Background: The prediction of response to immunotherapy mostly depends on the programmed death-ligand 1 (PD-L1) immunohistochemistry (IHC) status, and the 22C3 pharmDx assay has been approved in esophageal squamous cell carcinoma (ESCC). However, the widespread use of the 22C3 pharmDx assay is limited due to its availability. Thus, alternative PD-L1 assays are needed. We aimed to investigate the analytical and clinical diagnostic performances of four PD-L1 assays and to compare their concordances with the 22C3 pharmDx assay. Methods: The PD-L1 22C3 pharmDx assay was performed on the Dako Autostainer Link 48 platform, three testing assays (PD-L1 E1L3N XP antibody [Ab], PD-L1 BP6099 Ab and PD-L1 CST E1L3N Ab) on the Leica BOND-MAX/III platform, and one testing assay (PD-L1 MXR006 Ab) on the Roche VENTANA Benchmark Ultra platform. A total of 218 ESCC cases from four centers were included in this retrospective study. Professionals from each center stained and read the IHC slides independently and determined the combined positive score (CPS) and the tumor proportion score (TPS). Results: Regarding analytical performance, the four testing assays demonstrated good correlations with the 22C3 pharmDx assay when evaluated by the TPS or CPS (ρ > 0.8 for all four assays). Regarding diagnostic performance (CPS ≥ 10 was used as the cutoff), the four testing assays showed moderate concordances with the 22C3 pharmDx assay (kappa > 0.7 for all four assays). The overall percent agreements between each testing assay and the 22C3 pharmDx assay was at least 87.2 %. Conclusion: This study provides insight into the potential interchangeability of the four PD-L1 assays with the 22C3 pharmDx assay.