PDCD1LG2 and neoplasm: PD-L1 expression on the surface of tumor cells can attenuate the ability of the immune system to successfully eliminate tumor cells because the binding of the PD-1 receptor to its ligands, namely, PD-L1 and/or PD-L2, negatively regulates T-cell receptor (TCR) signaling, resulting in the inhibition of cytotoxic T lymphocytes [8].