PDCD1 and neoplasm: Immune checkpoint blockade (ICB) therapy has proven to be a transformative treatment option for a variety of cancers.1, 5 By blocking inhibitory receptors, most commonly programmed cell death protein-1 (PD-1), programmed death-ligand 1 (PD-L1) or cytotoxic T-lymphocyte associated protein 4 (CTLA-4), T cell function is improved, thereby enabling these cells to more effectively combat a patient’s tumor.6, 9 Even though the clinical benefit of ICB is unprecedented, the majority of patients fail to respond durably to this treatment, because of several types of resistance.5 10 11