Interlaboratory-Concordance Of Pd-L1 Ihc For Nsclc

e20508 Background: Immunohistochemistry (IHC) of the PD-L1 protein has become a mandatory diagnostic test for NSCLC. We conducted a two-step round robin test to analyze interobserver- and interlaboratory-concordance of PD-L1 IHC and to compare four clinical trial assays (CTAs; 28-8, 22C3, SP264, SP142) and laboratory-developed tests (LDTs). Results of step-one showed that reproducible PD-L1 IHC scoring is feasible; here we present the data on interlaboratory concordance Methods: Interlaboratory-concordance was tested by a centrally prepared tissue-microarray containing 21 NSCLC specimens that was stained at ten sites using CTAs and LDTs. Assay-performance was assessed with a second tissue-microarray containing eleven cell-lines with defined PD-L1 expression. Slides were evaluated by central quality-control and image-analysis. Results: The four CTAs yielded reproducible IHC-stainings at all sites while the results of the LDTs were mixed: Six protocols showed appropriate IHC quality with staining patterns similar to 22C3 and 28-8 CTAs, five protocols yielded less DAB-deposits and reduced staining intensity. Interlaboratory-concordance of carcinoma cell scoring using the 6-step system was moderate (κ = 0.43-0.69) while the included cut-offs ≥1% and ≥50% showed substantial concordance for the CTAs (κ = 0.73-0.89) and moderate concordance for the LDTs (κ = 0.50). No significant differences in interlaboratory-concordance were found among the CTAs. However, differences in the resulting staining patterns were noticed: While 22C3 and 28-8 showed similar staining patterns, SP263 showed minor differences in some cases and SP142 showed distinct patterns. Conclusions: The data show that the PD-L1 CTAs can be reproducibly employed and scored at different sites. LDTs with staining patterns similar to the CTAs are possible yet have to be carefully calibrated to match the appropriate intensity-range. The choice of assay and the set-up of the IHC-protocol may strongly influence the resulting staining.