In the past decade, rapid progress has been made in the development of immune checkpoint inhibitors (ICIs), such as programmed cell death protein 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) inhibitors and cytotoxic T-lymphocyte-associated protein 4 (CTLA4) inhibitors, have become a revolutionary cancer treatment method, providing long-term efficacy and survival benefits for a large number of cancer patients [25]. The gene discussed is PDCD1; the disease is cancer.