CD274 and skin cancer: PD-L1 is widely expressed on tumor cells and stromal cells such as TAMs, dendritic cells (DCs), and Langerhans cells (LCs) to maintain the immunosuppressive microenvironment in various skin cancers [23,61,62,63,64,65], not only melanoma [23], but also cutaneous SCC [61,62], Merkel cell carcinoma [63], EMPD [64,65], and CAS [66].