NKTL net score and group stratification. A flow cytometry net score ranging from −2 to 8 was calculated for each patient as follows: (sum of each activating ligand RFI score) − (sum of each inhibitory ligand RFI score). The histogram represents the distribution of patients according to their net score. A further stratification was performed in order to correlate NKRL expression to clinical outcome: patients were split into 2 homogeneous groups according to their flow cytometry net score: group 0 (G0) with score −2 to 1 and group 1 (G1) with score 2 to 8.