Interlaboratory concordance of PD-L1 immunohistochemistry for non-small-cell lung cancer

Abstract

Aims Programmed death ligand 1 ( PD ‐L1) immunohistochemistry has become a mandatory diagnostic test in the treatment of lung cancer. Several research initiatives have started to harmonise the five PD ‐L1 immunohistochemistry assays that have been used in clinical trials. Here, we report data on interlaboratory and interassay concordance for commercial assays (‘assays’) and laboratory‐developed tests ( LDT s) at 10 German testing sites. Methods and results To assess interlaboratory concordance, a tissue microarray containing 21 pulmonary carcinoma specimens was centrally prepared. Pre‐cut sections were stained at 10 sites by the use of assays 28‐8, 22C3, SP 263, and SP 142, as well as 11 LDT s. Assay performance was evaluated with a second tissue microarray containing 11 cell lines with defined PD ‐L1 expression. Quality control was centrally performed by manual and digital analyses. The assays yielded reproducible IHC staining patterns at all sites. In agreement with previous studies, 22C3, 28‐8 and SP 263 showed similar staining patterns, whereas SP 142 was distinct. Among the LDT s, six of 11 protocols showed staining patterns similar to those of assays 22C3 and 28‐8. Interlaboratory concordance of tumour cell scoring by use of a six‐step system was moderate (Light's κ = 0.43–0.69), whereas the clinically approved cut‐offs of ≥1% and ≥50% showed substantial concordance (κ = 0.73–0.89). Immune cell scoring by the use of SP 142 yielded moderate concordance (κ = 0.42). Conclusions The data confirm the previously described staining patterns of the assays, and show that they can be reproducibly employed at different sites. LDT s with staining results similar to those of the assays are implementable, but have to be carefully validated.