Natural killing activity is associated with progression of gastric cancer.

Previously, we proposed a new analysis of natural killing activity, in which an individual effector/target cell ratio was employed for comparison according to the peripheral number of effector cells. In 51 patients with gastric cancer, the activity was studied using that modified analysis. Natural killing activity was activated in patients with early cancer, where tumor-cell invasion was restricted to the mucosa or the submucosa, even though in well-differentiated adenocarcinoma with invasion of the mucosa alone, the activity remained at the level of controls. In contrast, the activity in advanced cancer, where tumor cells infiltrated beyond the submucosa, came to be inactivated as the cancer progressed. These facts suggest that natural killing activity in patients with gastric cancer is closely associated with tumor invasion and that reactive activation of the activity against tumor is induced, at least, in some patients with early stage.