Recently, the physiological functions in tumor surveillance of NK cells, as well as the therapeutic potential of many NK cell surface receptors, have been illustrated (e.g., KIR, TIGIT, NKG2A, CD96, and PD-1), while those of many others remain to be shown (e.g., LAG-3 and TIM-3) [106]. This evidence concerns the gene PDCD1 and neoplasm.