CD274 and Merkel cell skin cancer: Currently, the FDA has approved three PD-L1 inhibitors, which are Atezolizumab (MPDL3280), Durvalumab (MEDI4736), and Avelumab (MSB0010718C) (Figure 1), that are being used to treat different cancer types such as NSCLC and Merkel cell carcinoma (MCC) [83].