CD274 and melanoma: The surrounding niche of melanoma, that is, the tumour microenvironment (TME), is composed of fibroblasts, endothelial cells, extracellular matrix (ECM), various immune cells, such as tumour infiltrating lymphocytes (TILs), as well as interactions with human leukocyte antigen class I antigens (HLA-1) expressed on tumour cells, and other tumour-associated factors, such as PD-L1, which together play a crucial role in melanoma development (12–15).