According to the current clinical data, own unpublished data by using the primary melanoma model MT/ret, which spontaneously induces multiple cutaneous melanoma and distant organ metastases, including the CNS, show that inhibition of the PD-1/PD-L1 axis resulted in diminished intracranial tumor load but failed to suppress the establishement of micrometastases in the CNS (Helfrich, unpublished data) (61, 62). This evidence concerns the gene PDCD1 and melanoma.