PD-L1 and PD-L2 expressed by tumor cells bind to the PD-1 receptor on T cells, causing the inhibition of T cell activation, and the subsequent T cell attack is prevented, providing tumor cells with a means to escape the body’s immune surveillance and develop a tumor microenvironment beneficial for its uncontrolled proliferation [37] (Figure 1). This evidence concerns the gene PDCD1LG2 and neoplasm.