PDCD1 and neoplasm: In addition, a programmed death protein ligand 1 (PD-L1) inhibitor (e.g., PD1) has also been employed for immunotherapy of TNBC because the PD-L1 inhibitor can block the binding of PD1 on T cells with PD-L1 on tumor cells, which makes tumor cells reidentified and killed by T cells [33], but their efficacies are just passable [34].