Results: In breast cancer, the activity of GGT (+17.6%, p < 0.0001), catalase (+14.7%, p = 0.0485), urea content (+24.6%, p = 0.0006), total protein (+13.6%, p = 0.0432), α-amino acids (+3.1%, p < 0.0001) increased in saliva, but LDH activity (−16.9%, p < 0.0001) and the content of imidazole compounds (−25.2%, p < 0.0001) decreased. The gene discussed is CAT; the disease is breast carcinoma.