PDCD1 and skin squamous cell carcinoma: Antibodies targeting the PD-1/PD-L1 pathway are already approved to treat various human cancers, such as head and neck cancer (pembrolizumab and nivolumab), melanoma (pembrolizumab and nivolumab), urothelial carcinoma (nivolumab, pembrolizumab, durvalumab, atezolizumab, and avelumab), non-small cell lung cancer (pembrolizumab, nivolumab, and atezolizumab), renal cell carcinoma (nivolumab), Hodgkin lymphoma (pembrolizumab and nivolumab), skin squamous cell carcinoma (cemiplimab), and so on [315, 316].