Concordance between Three {PD}-L1 Immunohistochemical Assays in Head and Neck Squamous Cell Carcinoma ({HNSCC}) in a Multicenter Study

The introduction of immunotherapy targeting the programmed death-1 (PD-1)/programmed death-ligand-1 (PD-L1) axis has represented a turning point in the treatment of HNSCC. Harmonization studies comparing the different antibodies and immunohistochemistry platforms available for the evaluation of PD-L1 expression with Combined Positive Score (CPS) in HNSCC are strongly required. Tissue microarrays (TMA) constructed from formalin-fixed, paraffin-embedded (FFPE) tissue blocks of HNSCC tumor were stained with two commercial in-vitro diagnostic (IVD) PD-L1 immunohistochemical assays (22C3 pharmDx on Autostainer Link48 and Omnis platforms, and SP263) and were reviewed by seven trained pathologists to assess CPS. We found a very similar distribution for PD-L1 expression between 22C3 pharmDx assay with both platforms and SP263 assay and a strong significant correlation between the two assays in different platforms (p < 0.0001). The interobserver reliability among pathologists for the continuous scores of CPS with intraclass correlation coefficient (ICC) and the correlation between the two assays were both good. Moreover, the agreement rate between assays was high at all cut-offs, while the kappa values were from substantial to almost perfect. These data suggest the interchangeability of the two antibodies and of the different immunohistochemical platforms in the selection of patients with HNSCC for immunotherapy.