Nonetheless, due to PD-1 signaling is always mediated via engagements of PD-L1 or PD-L2 ligands and tumor environments are complex, the mechanism by which tumor cell-intrinsic PD-1 promotes CRC tumor growth is not only limited to the AKT and ERK signals, more about the principles among this process need to be further investigated. This evidence concerns the gene PDCD1 and neoplasm.