PDCD1 and cancer: Three different groups of ICIs, including PD-1 inhibitors (Nivolumab, Pembrolizumab, and Cemiplimab), PDL-1 inhibitors (Atezolimumab, Durvalumab and Avelumab), and CTLA-4 inhibitor (Ipilimumab) have been approved by the US Food and Drug Administration (FDA) for the treatment of various types of cancer [5].