Koomen BM, et al. - This systematic review recognizing publications that estimated inter-assay, inter-observer and/or inter-laboratory concordance of programmed death-ligand 1 (PD-L1) assays and laboratory-developed tests (LDTs) in the tissue of non-small cell lung cancer (n = 4,294 publications pooled, 27 involved) was performed in order to give a current insight into the comparability of standardized immunohistochemical assays and LDTs, concentrating exactly on tumor cell staining and scoring. The interchangeability of PD-L1 immunohistochemistry assays and LDTs was hampered by a reduction in inter-assay concordance with the use of clinically appropriate cut-offs. Furthermore, in clinical practice, the use of the 1% cut-off could be problematical, as discordance between pathologists at this cut-off may lead to some individuals being refused relevant treatment alternatives.