|PD-L1 is an important immunopharmacological drug discovery target., as many types of cancer cells express this ligand [1-2,5]. Expression of cell-surface PD-L1 permits malignant cells to 'evade' destruction by the immune system by inhibiting T-cell-mediated responses. Antibodies directed against PD-L1 are emerging as novel cancer therapeutics. This list of clinical trials assessing MPDL3280A, just one ant-PD-L1 agent, gives an idea of the range of cancers that may respond to this mechanism of drug action. See also  and .