Immune checkpoint inhibitors (ICI) (anti-CTLA-4, anti-PD-1, anti-PD-L1) may constitute a breakthrough in terms of a new type of immunotherapy in the treatment of cancer as they have contributed to improvement in the prognosis of patients with neoplasms, such as melanoma, non-small cell lung cancer (NSCLC), urothelial carcinoma, renal cell carcinoma, head and neck squamous cell cancer (HNSCC), or neoplasms of the lymphatic system—Hodgkin’s lymphoma. The gene discussed is PDCD1; the disease is cancer.