Although recent data show therapeutic activity against melanoma BM by targeting the BRAF pathway or by immune checkpoint inhibition using inhibitors against the cytotoxic T-lymphocyte-associated Protein 4 (CTLA-4) or the Programmed cell death protein 1 (PD-1), response rates are rather limited and, overall, patients still have a poor prognosis [30,31]. Here, PDCD1 is linked to melanoma.