PD-L1 immunohistochemistry comparison of 22C3 and 28-8 assays for gastric cancer

BackgroundNivolumab and pembrolizumab are promising therapies for gastric adenocarcinoma. The 22C3 and 28-8 pharmDx immunohistochemistry assays for programmed death ligand-1 scoring criteria have been developed. This study compared the programmed death ligand-1 staining patterns of gastric adenocarcinoma evaluated by the 22C3 and 28-8 pharmDx assays.MethodsTissue microarray analysis was performed for 226 patients with gastric adenocarcinoma who underwent curative surgery. Interobserver concordance between the 22C3 and 28-8 pharmDx assays was assessed to compare the dichotomized expression values. Programmed death ligand-1 positivity was assessed by combined positive score and tumor proportion score. Immunohistochemistry for deficient mismatch repair proteins and Epstein-Barr virus-encoded RNA in situ hybridization was examined.ResultsProgrammed death ligand-1 positivity with a combined positive score ≥5 was detected in 63 patients (28%) by the 22C3 pharmDx assay, and in 45 patients (20%) by the 28-8 pharmDx assay. A pairwise comparison of the 22C3 and 28-8 pharmDx assays showed 87% of pairs were concordant and 11% higher expressions for the 22C3 pharmDx assay, with strong concordance (kappa score =0.881 with a combined positive score cutoff of 5). The programmed death ligand-1 positivity rate (range, 3–5%) of the tumor proportion score was markedly lower than that of the combined positive score in the two assays. Programmed death ligand-1 positivity of the combined positive score in these two assays was associated with mismatch repair proteins and Epstein-Barr virus status. There was no significant difference in the overall survival between programmed death ligand-1, mismatch repair proteins, and Epstein-Barr virus status.ConclusionsThe study findings suggest the potential interchangeability of the 22C3 and 28-8 pharmDx assays to determine programmed death ligand-1 expression levels in gastric adenocarcinoma patients.