PDCD1 and cancer: Immune escape is considered one of the cancer hallmarks.[47] PD1 is a typical immune checkpoint mediating immune escape for cancer cells because its binding with PD-L1 from tumor cells results in the inhibition of CD8 T-cell tumor-killing activity.[48] However, the binding between PD-1 and PD-L1 also shields normal cells from being attacked by the immune system, which potentially explains the toxicity from PD-1/PD-L1 target therapy.[49]