PDCD1 and cancer: Currently, ICIs approved by the US Food and Drug Administration (FDA) for the treatment of various types of cancer include PD-1 inhibitors (nivolumab, pembrolizumab, and cemiplimab), PD-L1 inhibitors (atezolizumab, durvalumab, and avelumab), and a CTLA-4 inhibitor (ipilimumab) [4].