CD274 and Merkel cell skin cancer: Within the past 3 years, four monoclonal antibodies targeting the PD-1-PD-L1 axis have been approved by the FDA for use: nivolumab (anti-PD1, approved in melanoma, NSCLC, renal cell carcinoma, Hodgkin lymphoma, head and neck squamous cell carcinoma (HNSCC), urothelial carcinoma), pembrolizumab (anti-PD-1, approved in melanoma, NSCLC, HNSCC, Hodgkin lymphoma,) atezolizumab (anti-PD-L1, approved in urothelial cell carcinoma and NSCLC) and avelumab (anti-PD-L1, approved in Merkel cell carcinoma).