PDCD1 and cancer: The expression of programmed death-ligand 1 in cancer cells sends inhibitory signals to T cells through programmed cell death protein 1 (PD-1), allowing tumor cells to evade the immune system.[1] The anti-PD-1 antibody pembrolizumab activates tumor-specific CD8+ T cells, and has been approved for the treatment of patients with advanced urothelial carcinoma.