While PD-1 inhibitors block the interaction between PD-1 and PD-L1 and, respectively, PD-L2, PD-L1 blockers inhibit only the PD-1/PD-L1 axis, allowing the tumor cells to escape the immune system via PD-1-PD-L2 axis and thus explaining the abovementioned results [58]. This evidence concerns the gene PDCD1 and neoplasm.