In peripheral blood, the level of NKG2D, an activating receptor, was increased, and the level of NKG2A, a known inhibitory receptor, was significantly decreased in patients with ESCC compared with healthy volunteers (p < 0.05) (Fig. 2a and b), suggesting that the activity of NK cells was enhanced. The gene discussed is KLRC1; the disease is esophageal squamous cell carcinoma.