PDCD1 and cancer: Cancer treatment was revolutionized by the introduction of immune checkpoint inhibitors (ICIs) in 2011.1,2 These humanized monoclonal antibodies block molecules that regulate T-cell function such as cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death 1 (PD-1) or their ligands,2 thereby promoting T-cell response to eradicate cancer cells.