Evaluation of programmed death-ligand 1 (PD-L1) expression
tumor
CPS, SECONDARY, TUMOR
PD-L1 expression was evaluated using immunohistochemistry (Ventana PD-L1, SP263). SP263 is a recombinant rabbit monoclonal antibody that binds to PD-L1 in paraffin-embedded tissue sections. Specific antibody localization can be performed by haptenated secondary antibodies in combination with multimeric anti-hapten-horseradish peroxidase (OptiVIEW DAB IHC Detection Kit). The specific antibody–enzyme complex is then visualized with a precipitating enzyme reaction product. The combined positive score (CPS) was used to evaluate the PD-L1 expression and was calculated as follows: the number of PD-L1-stained cells (tumor cells and related immune cells) divided by the total number of viable tumor cells, multiplied by 100. PD-L1 was considered to be expressed if the CPS was ≥ 1.