A Prospective, Multi-institutional, Pathologist-Based Assessment of 4 Immunohistochemistry Assays for PD-L1 Expression in Non–Small Cell Lung Cancer

Abstract

Importance Four assays have been registered with the FDA to detect PD-L1 to enrich for patient response to anti-PD-1/PD-L1 therapies. The tests use four separate PD-L1 antibodies on two separate staining platforms and have their own scoring systems which raises questions about their similarity and potential cross-utilization. Objective We compared the performance of four PD-L1 platforms, including two FDA-cleared assays and two laboratory developed tests (LDTs). Design Four serial histology sections from 90 archival NSCLCs were distributed to three sites that performed the following IHCs: 1) 28-8 antibody on Dako Link 48; 2) 22c3 antibody on Dako Link 48; 3) SP142 antibody on Ventana Benchmark; and 4) E1L3N antibody on Leica Bond. Slides were scanned and scored by thirteen pathologists by estimating the percentage of malignant and immune cells expressing PD-L1. Intraclass correlation coefficients (ICC) and paired and mixed effects statistical analyses were performed to compare antibodies and pathologists scoring of tumor and immune cells. Results The SP142 Ventana assay was an outlier with a significantly lower mean score of PD-L1 expression in both tumor and immune cells. Pairwise comparisons showed the 28-8 and E1L3N were not significantly different, but that 22c3 showed a slight but statistically significant reduction in tumor cell labeling. Evaluation of ICC between antibodies to quantify inter-assay variability using the average of thirteen pathologists scores for tumor shows very high concordance between antibodies for tumor cell scoring (0.813) and lower levels of concordance for immune cell scoring (0.277). When examining inter-pathologists variability for any single antibody, the concordance between pathologists’ reads for tumor ranged from ICC of 0.83 to 0.88 for each antibody while the ICC from immune cells for each antibody ranged from 0.17 to 0.23. Conclusions The assay using the SP142 antibody is a clear outlier detecting significantly less tumor cell and immune cell PD-L1 expression. Antibody 22c3 shows slight yet statistically significantly lower staining than either 28-8 or E1L3N, but this significance is only detected when using the average of thirteen pathologist scores. Pathologists show excellent concordance when scoring tumor cells stained with any antibody, but poor concordance for scoring immune cell staining.

PD-L1 protein expression in non-small cell lung cancer based on different immunohistochemical antibodies

“…Third, it only compares the performance of four PD-L1 platforms; there are no therapeutic outcome data to evaluate the clinical predictive power of alternative PD-L1 IHC testing strategies. Recent United States-based study concurs with the Blueprint study (12). This study was funded by pharmaceutical companies (Bristol-Myers Squibb) and the NCCN oncology research programme.…”

Current Landscape of Immunotherapy for the Treatment of Metastatic Non-Small-Cell Lung Cancer

“…The latter finding is supported by another study that suggested that SP142 might have higher specificity, but lower sensitivity, when compared with 22C3 and that it typically underestimated PD-L1 scores for treatment with pembrolizumab 20 . A prospectively designed, statistically powered trial assessed 4 assays, including 22C3, E1L3N, 28-8, and SP142, and found the SP142 assay to be an outlier, detecting significantly less PD-L1 expression in tumour cells; however, excellent concordance and reproducibility between the other 3 assays was demonstrated, with the authors concluding that they were equivalent 21 . Although excellent concordance was seen when samples were obtained from tumour cells, greater variability was observed when scoring immune cells with any antibody 20,21 .…”

Immune Checkpoint Blockade: The New Frontier in Cancer Treatment

“…Variability in PD-L1 testing can arise because of the type (tumor cells, immune cells, or a combination) and percentage cutoffs used for positivity, archival versus fresh tissue, primary versus metastatic biopsies, diversity of antibodies utilized, and tumor heterogeneity [86,87]. Several comparative studies across different PD-L1 assays have been conducted, including collaborative studies between industry and academic institutions [88][89][90][91]. The outcomes of these studies have varied, with two studies showing concordance among assays [88,90], one study showing equivalence for most assays [91], and one study revealing differences across all of the assays that do not support interchangeability [89].…”

“…Several comparative studies across different PD-L1 assays have been conducted, including collaborative studies between industry and academic institutions [88][89][90][91]. The outcomes of these studies have varied, with two studies showing concordance among assays [88,90], one study showing equivalence for most assays [91], and one study revealing differences across all of the assays that do not support interchangeability [89]. Based on these preliminary findings, the PD-L1 assays that are currently available are not considered interchangeable.…”