Because of the different contribution of adaptive and innate cytotoxic lymphocytes in anti-tumour response, it is crucial to further dissect the molecular mechanisms, the timing and the clinical conditions driving PD-1 expression on NK cells in depth, to better understand how to unleash NK cells’ anti-tumour function by blocking the PD-1/PD-L1 activity. The gene discussed is PDCD1; the disease is neoplasm.