PDCD1 and cancer: The early 2000s saw the emergence of immune checkpoint inhibitors, with the FDA approval of anti-CTLA-4 (cytotoxic T lymphocyte-associated protein 4) (ipilimumab) in 2011 and anti-PD-1/PD-L1 (programmed cell death protein 1) (nivolumab, pembrolizumab) in 2014, revolutionizing cancer treatment by enhancing the body’s natural immune response.5