Downes MR, et al. - Using three commercial clones (SP263, SP142, 22C3) and one platform-independent test (E1L3N), PD-L1 expression in tumour cells and immune cells (IC) was manually scored in 27 head and neck squamous cell carcinoma (HSCC), 30 urothelial carcinomas (UC) and breast carcinoma (BC) in order to evaluate pathologist consistency in assessing PD-L1 immunopositivity by exploring the inter- and intraobserver agreement using different antibody clones and various cancer types. The percentage of PD-L1 positive cases was dependent profoundly on the algorithm/cut-off values used. Using SP263 and E1L3N in HSCC, 22C3, SP142, and E1L3N in BC and 22C3 in UC, almost excellent interobserver agreement was attained. The SP142 clone in UC and HSCC exhibited moderate agreement and was correlated with lower ICC and reduced intraobserver concordance. In conclusion, outstanding inter- and intraobserver agreement can be accomplished using SP263, 22C3, and E1L3N, whereas PD-L1 scoring using SP142 clone is related to a greater level of subjectivity.