CD274 and Merkel cell skin cancer: Immune checkpoint blockade agents targeting either Cytotoxic T Lymphocyte Antigen-4 (CTL-4) or Programmed Cell Death/Ligand-1 (PD-1/PD-L1), that can unleash anti-tumor immune responses, have been approved for the treatment of different solid tumors, e.g., melanoma, lung, head and neck cancer, bladder, and Merkel cell cancer, as well as some hematological malignancies [5].