In particular, systemic treatment with the monoclonal antibodies ipilimumab, which targets the T-lymphocyte-associated protein 4 (CTLA-4), as well as nivolumab and pembrolizumab, which target the programmed cell death protein 1 (PD-1), has led to unprecedented response and survival rates in advanced melanoma and is nowadays considered the first-line therapy for unresectable stage III and IV melanoma patients [1,2,3,4,5,6,7]. Here, PDCD1 is linked to melanoma.