PD-L1 Expression Harmonization in Gastric Cancer Using 22C3 PharmDx and SP263 Assays

The immune checkpoint inhibitor Pembrolizumab has been FDA-approved for the treatment of gastric cancer (GC) and gastroesophageal junction (GEJ) cancer in patients who fail second-line therapy and test positive by a companion programed death ligand 1 (PD-L1) assay, the 22C3 PharmDx. It would be useful to investigate the potential interchangeability of other PD-L1 assays in order to develop a more sustainable diagnostic strategy. We investigated the possibility of harmonizing different PD-L1 assays, utilizing samples from 94 GC and GEJ patients to compare their expression using 2 laboratory developed tests (LDTs): The Dako 22C3 antibody and the Ventana SP263 run on the Ventana platform with the FDA-approved companion diagnostic test, the 22C3 PharmDx. This would be the first report assessing the 22C3 on Ventana's platform in GC. Pearson correlation coefficients between the Dako 22C3 PharmDx and the 22C3-LDT and the Ventana SP263 assays were 0.965 (P<0.001) and 0.932 (P<0.001), respectively, which indicates an almost perfect correlation. The sensitivity and specificity were also high at different cutoffs [both 100% at combined positive score (CPS)≥1 and 92.59% and 95.52% at CPS≥10, respectively] for the comparison between Dako 22C3/22C3-LDT assays. As for the sensitivity and specificity between the Dako 22C3/Ventana SP263 assays the results were 100% and 95.67% at CPS≥1; and 96.30% and 95.52% at CPS≥10, respectively. In conclusion, the analytical performance of 22C3 and SP263 clones on the Ventana platform was close to that of the reference assay (Dako 22C3 assay), suggesting that the 2 LDTs can be utilized interchangeably with the FDA-approved standard assay as an aid to select GC and GEJ patients for Pembrolizumab treatment.