Harmonization across programmed death ligand 1 (PD‐L1) assays for lung cancer by immunohistochemistry using noncontact alternating current electric field mixing

BACKGROUND: Immune checkpoint inhibitors (ICIs) are a promising advance in the treatment of patients with lung cancer. However, each ICI has been tested with an independently designed companion diagnostic assay that is based on a unique antibody. Consequently, the different trial‐validated programmed death ligand 1 (PD‐L1) immunohistochemistry (IHC) assays should not be considered interchangeable. Our aim was to compare the performance of each available PD‐L1 antibody for its ability to accurately measure PD‐L1 expression and to investigate the possibility of harmonization across antibodies through the use of a new rapid IHC system, which uses noncontact alternating current (AC) mixing to achieve more stable staining. METHODS: First, 58 resected non‐small cell lung cancer (NSCLC) specimens were stained using three PD‐L1 IHC assays (28–8, SP142, and SP263) to assess the harmonization achieved with AC mixing IHC. Second, specimens from 27 patients receiving ICIs for postoperative recurrent NSCLC were stained using the same IHC method to compare the clinical performance of ICIs to PD‐L1 scores. All patients received a tumor proportion score (TPS) with the 22C3 companion diagnostic test. RESULTS: Better staining was achieved with the new AC mixing IHC method than the conventional IHC in PD‐L1‐positive cases, and the interchangeability of some combinations of assays was increased in PD‐L1‐positive. In addition, AC mixing IHC provided more appropriate overall response rates for ICIs in all assays. CONCLUSIONS: Stable PD‐L1 IHC driven by AC mixing helped to improve TPS scoring and patient selection for ICIs through interchangeable assays.