Chronic restraint stress led to an elevation in the expression level of iNOS and 4HNE, and a significant reduction in the protein expression of SOD2, and chewing during the chronic restraint stress caused reduction in the protein expression of iNOS and 4HNE, and elevation in the protein expression of SOD2 in comparison with the stress group (p < 0.01, Figure 5), suggesting that chewing behavior during psychological stress reduced oxidative stress in the tumor. This evidence concerns the gene SOD2 and neoplasm.