PDCD1 and melanoma: Targeting the programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) and the cytotoxic T lymphocyte antigen-4 (CTLA-4) axis through the development of ICB therapies has revolutionised the management of several solid tumours over the past decade, such as melanoma and non-small cell lung cancer (NSCLC).