Immunotherapy using immune checkpoint inhibitors (ICIs), such as antibodies against PD-1 or cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), has recently emerged as a potential treatment for various malignancies, and PD-1/PD-L1 inhibitors have been approved by the Food and Drug Administration (FDA) as the first- or second-line treatments for urothelial carcinoma [11–14]. The gene discussed is PDCD1; the disease is urothelial carcinoma.