Some PD-1/PD-L1 checkpoint inhibitors are currently available commercially; however, due to tumor heterogeneity and tumor-intrinsic resistance mechanisms, such as altered IFN signaling pathways, increased mutations, defective antigen presentation, and drug-resistant gene expression, the clinical response rate of PD-1/PD-L1 therapies is approximately 30%80. The gene discussed is PDCD1; the disease is neoplasm.