Antibodies that target programmed cell death protein 1 (PD-1) or one of its ligands, programmed death-ligand 1 (PD-L1) (e.g., nivolumab, pembrolizumab, atezolizumab, avelumab, durvalumab), are active against a broad range of malignancies and are changing the treatment landscape for cancer. Here, PDCD1 is linked to cancer.