PDCD1 and melanoma: Figure 4B shows representative mIF images of stage I and stage III melanoma-infiltrated areas. We used these infiltrated areas to evaluate the expression of PD-1 and PD-L1. We observed that PD-1 expression is restricted to the infiltrated areas, whereas PD-L1 is expressed both in the infiltrating and tumor cells, but it is especially highly expressed in the latter. We also found that the percentage of PD-1 and PD-L1 positive cells was similar in both types of melanoma at early (I/II) and late stages (III/IV) (Figure 4C,D).