Analytical comparison of a PD-L1 22C3 antibody laboratory-developed test (LDT) protocol on the benchmark XT and PD-L1 IHC 22C3 pharmdx: analysis of pan-tumour and oesophageal cancer samples

PD-L1 IHC 22C3 pharmDx is an FDA-approved companion diagnostic to pembrolizumab designed for use on Autostainer Link 48. We compared our PD-L1 22C3 antibody-based LDT1 on BenchMark XT with PD-L1 IHC 22C3 pharmDx. Head and neck squamous cell carcinoma (HNSCC), urothelial carcinoma (UC), and oesophageal SCC (ESCC) tumour specimens were stained with 22C3 antibody, scored using the LDT on BenchMark XT, and compared with PD-L1 IHC 22C3 pharmDx. PD-L1 was measured using combined positive score (CPS) and standard cutoffs (HNSCC, ≥1; UC, ≥10; ESCC, ≥10). 327 samples were evaluated (HNSCC, n=126; UC, n=121; ESCC, n=80). Pan-tumour intraclass correlation coefficient (ICC) of PD-L1 CPS as a continuous variable was 0.96 (95% CI, 0.95–0.97); Spearman correlation was 0.95. For ESCC, ICC was 0.92 (95% CI, 0.88–0.95); Spearman correlation was 0.89. Interpretation of PD-L1 status (CPS ≥10) for ESCC using the two assays resulted in NPA of 92% (95% CI, 80–97), PPA of 88% (95% CI, 74–95), and OPA of 90% (95% CI, 81–95). 22C3 antibody-based LDT on BenchMark XT demonstrated high concordance with PD-L1 IHC 22C3 pharmDx. These findings suggest comparability of PD-L1 IHC 22C3 pharmDx with an LDT based on the 22C3 antibody across several tumour types. 1.Neuman T, London M, Kania-Almog J, et al. A harmonization study for the use of 22C3 PD-L1 immunohistochemical staining on Ventana’s platform. J Thorac Oncol 2016; 11: 1863–8.