ERBB2 and neoplasm: Since both markers are expressed by tumor cells in the membrane compartment, the use of the invisible deposited chromogen to stain PD-L1 and DAB to stain HER2 helps distinguish the two biomarkers, even in the same compartment of co-expressing cells, whereas the use of two visible-light-absorbing deposited chromogens would obscure each other’s detection in cells with co-expression.