PDCD1 and non-small cell lung carcinoma: In addition, a subset of PD-1+ tumour-infiltrating NK cells was identified and characterized in non-small cell lung cancer (NSCLC): PD-1+ NK cells co-expressed more inhibitory receptors as compared to the PD-1− subset, and increasing levels of PD-1 expression correlated with intratumoural NK cell dysfunction [53].