CD274 and Merkel cell skin cancer: Apart from these, there are several PD-L1 immune checkpoint inhibitors approved by the Food and Drug Administration (FDA) in the USA for various cancers, for instance, atezolizumab for urothelial carcinoma and non-small cell lung carcinoma, ipilimumab for melanoma, and avelumab for Merkel cell carcinoma and urothelial carcinoma [19–21].