MKI67 and neoplasm: The percentage of Ki67-positive tumor cells in the stress group was markedly higher than that of the control and stress+chewing groups (p < 0.01, Figure 2C), and the protein expression of Ki67 in the stress+chewing group was significantly lower than that of the stress group (p < 0.01, Figure 2E), suggesting that chewing behavior during psychological stress remarkably reduced the tumor cell proliferation.