PDCD1 and cancer: Cancer immunotherapyaims to stimulate the immune system’sability to fight cancer as opposed to directly killing cancer cellswith more traditional methods such as chemotherapy and radiation therapy.1−6 Inhibition of negative immune checkpoint regulators is now usedin clinics around the world and was recognized with the 2018 NobelPrize in Physiology or Medicine.7 One ofthe most important immune checkpoints (ICs) in cancer immunotherapyconsists of programmed cell death protein 1 (PD-1, also known as CD279)with its ligand (PD-L1, known also as CD274 or B7-H1).4