Immune checkpoint inhibitors (ICIs) such as anti-programmed cell death protein-1 (PD-1)/programmed death ligand-1 (PD-L1) and anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) have been extensively studied for both primary and recurrent glioblastomas in medical research. The gene discussed is PDCD1; the disease is glioblastoma.