Verification and validation of the anti-PD-L1 antibody, Clone 22C₃ on a laboratory-developed test

The first aim of this study is to compare and validate the performance of the programmed death receptor ligand 1 (PD-L1) IHC 22C3 pharmDx assay kit processed via Dako Omnis platform with the Dako Autostainer Link 48. The second aim is to examine the concordance of scoring by pathologists using the same immunohistochemistry (IHC) assay on the Dako Omnis platform and the Dako Autostainer Link 48.

Fourty-seven formalin-fixed, paraffin-embedded tissue blocks of head and neck squamous cell carcinoma tumour were stained with the PD-L1 IHC 22C3 pharmDx assay kit processed via the Dako Autostainer Link 48 and the Dako Omnis platform. Combined positive score (CPS) was ascribed by two scoring pathologists, with discordant cases provided with an agreed score.

First, identical staining patterns were identified. Second, high agreement of PD-L1 scores when a CPS cut-off of 1 was implemented illustrated an overall agreement of 94%, positive agreement of 100% and negative agreement of 88%. Finally, results highlight an intraexaminer concordance of 89% and interexaminer concordance of 85% and 92%.

In conclusion, we propose to open for discussion the deconstruction of the current practice of a compulsory companion diagnostic test (CDT) for a particular PD-L1 immunohistochemical assay. The implementation of laboratory developed tests as an alternative to the CDT poses as a novel and readily available method to surmount limitations posed to pathology laboratories.