Background: In recent years, a range of cancers have been demonstrated to interfere and effectively evade the adaptive immune response by hijacking immune checkpoints and expressing proteins able to activate them. PD-L1, a ligand protein that binds programmed death receptor 1 (PD-1) in cells of the adaptive immune system and the discovery that a range of tumours exploit this pathway to avoid immune detection has led to an effort in its targeting by immunotherapy.