External quality assessment demonstrates that PD‐L1 22C3 and SP263 assays are systematically different

Abstract

PD-L1 inhibitors are part of first line treatment options for patients with advanced non-small cell lung cancer. PD-L1 immunohistochemistry (IHC) assays act as either a companion or a complementary diagnostic. The purpose of this study is to describe the experience of external quality assurance (EQA) provider UK NEQAS ICC and ISH with the comparison of different PD-L1 assays used in daily practice. Three EQA rounds (pilot, run A and run B) were carried out using formalin fixed paraffin embedded samples with sample sets covering a range of epitope concentrations, including 'critical samples' near to clinical threshold cut-offs. An expert panel (n = 4) evaluated all returned slides simultaneously and independently on a multi-header microscope together with the participants own in-house control material. The tonsil sample was evaluated as 'acceptable' or 'unacceptable', and for the other samples the percentage of PD-L1 stained tumour cells were estimated in predetermined categories (<1%, 1 to <5%, 5 to <10%, 10 to <25%, 25 to <50%, 50 to <80%, 80 to 100%). In the pilot and the two subsequent runs the number of participating laboratories was 43, 69 and 76, respectively. The pass rate for the pilot run was 67%; this increased to 81% at run A and 82% at run B. For two 'critical samples', in runs A and B, 22C3 IHC had significantly higher PD-L1 expression than SP263 IHC (p < 0.001), whilst the PD-L1 scores for the other six samples were similar for all assays. In run A the laboratory developed tests (LDTs) using 22C3 scored lower than the commercial 22C3 tests (p = 0.01). After the initial testing, improvement in performance of PD-L1 IHC is shown for approved and LDT PD-L1 assays. Equivalency of approved PD-L1 22C3 and SP263 assays cannot be assumed as the scores cross the clinically relevant thresholds of 1% and 50% PD-L1 expression.

PD-L1 immunohistochemistry in non-small-cell lung cancer: unraveling differences in staining concordance and interpretation

“…Additional research into the different validation practices of the participants might provide a better insight as to why LDTs are currently underperforming. Some previous studies confirm our results, in which fewer LDTs passed the quality control compared with the clinically validated assays for PD-L1 [17,[27][28][29], and for ALK receptor tyrosine kinase IHC [35,36]. However, other studies reported a high concordance of LDTs with reference assays [21,37].…”

“…Irrespective of the protocol used, laboratories are required to appropriately verify or validate their PD-L1 IHC test, to take part in continuous quality monitoring and participation to External Quality Assessment (EQA) [24][25][26]. Lower staining concordance for LDTs compared with CE-IVD approved assays was reported by two other EQA providers [27][28][29], but participants' interpretation of the TPS was not always assessed [27]. The aim of this study is to evaluate the results of assessment of the staining concordance of PD-L1 IHC and its influence on TPS estimations, for the different (LDT or CDx approved) methods in two subsequent EQA schemes of the European Society of Pathology (ESP).…”

PD‐L1 in squamous cell carcinoma of the oral tongue shows gender‐specific association with prognosis

“…Accurate measurement and scoring of PD-L1 protein expression is difficult due to various technical and biological pitfalls (Topalian, Taube, Anders, & Pardoll, 2016), and the choice of immunohistochemical assays and scoring strategies could lead to discrepancies between different studies (Dodson et al, 2019;Lenouvel et al, 2019). Several PD-L1 diagnostic assays are commercially available, such as Ventana SP263 (durvalumab), Dako 22C3 (pembrolizumab), and Dako 28-8 (nivolumab).…”

Considerable interlaboratory variation in PD-L1 positivity in a nationwide cohort of non-small cell lung cancer patients

“…In contrast, a meta-analysis of diagnostic accuracy of PD-L1 IHC assays concluded that properly designed LDTs may in fact achieve higher accuracy than commercial PD-L1 assays, when both are compared to an appropriate reference standard [11]. Various other studies have shown substantial interlaboratory concordance of PD-L1 staining for several commercial PD-L1 assays [22,[39][40][41], while another study stated that equivalence of commercial PD-L1 assays at the 1% and 50% cutoff cannot be assumed [42]. Lastly, a study by Butter et al [43] showed a similar degree of interlaboratory concordance between laboratories using a 22C3 LDT and laboratories using the 22C3 pharmDx commercial assay (Agilent), but also concluded that interlaboratory variability of immunostaining contributes to discrepancies in PD-L1 positivity between centers.…”

“…This may not always be the case in all laboratories, which may suggest that use of commercial assays could also contribute to reduction of interlaboratory variability in PD-L1 positivity. Nevertheless, this remains uncertain, since even laboratories that use the same commercial assay can produce differences in PD-L1 staining results [38,43] and others have reported inequality of commercial assays at the 1% and 50% cutoff [42]. To help create more awareness among pathologists, results from individual laboratories in our study were sent back to these laboratories as feedback reports.…”