PDCD1 and melanoma: Immune checkpoint inhibitors (ICIs) targeting the programmed cell death 1 (PD1) and its ligand 1 (PD-L1) and the cytotoxic T-lymphocyte antigen-4 (CTLA-4) have revolutionized the treatment and prognosis of several solid and haematological malignancies, including lung, kidney, and urothelial cancers and melanoma and lymphoma [1,2].