KLRD1 and lung adenocarcinoma: In this respect, CCL5 gene expression highly correlated with PRF1, which encodes for perforin, a marker of NK cell activation (Spearman Rho = 0.76 and 0.828 in lung adeno-carcinoma and squamous, respectively; p < 0.001) and with NK cell receptor NKG7 (Spearman Rho = 0.908 and 0.859 in lung adeno-carcinoma and squamous, respectively; p < 0.001); a moderate correlation was detected for the NK receptor FCGR3A (Spearman Rho> 0.5; p < 0.001) (Fig. 2A).