Cancer cells have been shown to evade the host immune system by expressing high levels of immune inhibitory signaling proteins, such as programmed death ligand 1 (PD-L1).56 In recent studies, downregulation of the immune checkpoint PD-L1 was found to increase Chk in human breast and pancreatic cancer cells, and downregulation of Chk was found to increase PD-L1. This evidence concerns the gene CHKA and cancer.