A method of scoring PD-L1 expression in a tumor sample, the method comprising: • labeling the tumor tissue sample, the labeling comprising: ∘ contacting the tissue sample with an anti-PD-Ll primary antibody; and ∘ contacting the same tissue sample with ∘ a primary antibody directed to a tumor cell-specific marker and an antibody directed to an immune cell-specific marker; and ∘ visualizing each of the antibodies in the tissue sample with a reagent that generates a detectable signal corresponding to each of the primary antibodies, wherein the anti-PD-Ll antibody has a first detectable signal, the antibody directed to the tumor cell-specific marker has a second detectable signal distinguishable from the first detectable signal, and the antibody directed to an immune cell-specific marker has a third detectable signal distinguishable from the first detectable signal and the second detectable signal; wherein the first, second, and third detectable signals are generated by chromogens; and • scoring PD-L1 expression in tumor cells, immune cells, or both, wherein co-localization of the first and second detectable signals indicates the presence of PD-L1-positive tumor cells and co-localization of the first and third detectable signals indicates the presence of PD-L1-positive immune cells. • labeling the tumor tissue sample, the labeling comprising: ∘ contacting the tissue sample with an anti-PD-Ll primary antibody; and ∘ contacting the same tissue sample with ∘ a primary antibody directed to a tumor cell-specific marker and an antibody directed to an immune cell-specific marker; and ∘ visualizing each of the antibodies in the tissue sample with a reagent that generates a detectable signal corresponding to each of the primary antibodies, wherein the anti-PD-Ll antibody has a first detectable signal, the antibody directed to the tumor cell-specific marker has a second detectable signal distinguishable from the first detectable signal, and the antibody directed to an immune cell-specific marker has a third detectable signal distinguishable from the first detectable signal and the second detectable signal; wherein the first, second, and third detectable signals are generated by chromogens; and ∘ contacting the tissue sample with an anti-PD-Ll primary antibody; and ∘ contacting the same tissue sample with ∘ a primary antibody directed to a tumor cell-specific marker and an antibody directed to an immune cell-specific marker; and ∘ visualizing each of the antibodies in the tissue sample with a reagent that generates a detectable signal corresponding to each of the primary antibodies, wherein the anti-PD-Ll antibody has a first detectable signal, the antibody directed to the tumor cell-specific marker has a second detectable signal distinguishable from the first detectable signal, and the antibody directed to an immune cell-specific marker has a third detectable signal distinguishable from the first detectable signal and the second detectable signal; • scoring PD-L1 expression in tumor cells, immune cells, or both, wherein co-localization of the first and second detectable signals indicates the presence of PD-L1-positive tumor cells and co-localization of the first and third detectable signals indicates the presence of PD-L1-positive immune cells.