CD69 and neoplasm: Furthermore, there were significantly higher frequencies of PD-1+ and CD69+ NK cells in the tumour (n = 8–10) of OAC patients relative to the circulation (n = 17–20); PD-1: blood versus tumour (20.03% vs. 38.16%, p = 0.011), CD69: blood versus tumour (13.14% vs. 60.18, p < 0.0001) (Fig. 1b).