PDCD1 and colorectal carcinoma: Some of these have successfully paved their way to the clinic, for instance, immune checkpoint inhibitors directed against programmed cell death protein 1 (PD-1) or cytotoxic T lymphocyte-related protein 4 (CTLA-4) are effective against microsatellite-unstable CRC.7 Nevertheless, significant challenges remain, especially for microsatellite-stable CRC, which is characterized by a poor response to these checkpoint inhibitors.7