Since ipilimumab became the world-first approved immune checkpoint inhibitor (ICI) by the Food and Drug Administration, ICIs, mainly including monoclonal antibodies targeting PD-1, PD-L1, and CTLA-4, have been widely used and exhibited significant clinical activity in a spectrum of malignancies, including GC and CRC (156, 157). Here, PDCD1 is linked to colorectal carcinoma.