CAT and cancer: Decreased catalase activity in tumor cells may lead to the accumulation of H2O2, which causes DNA damage and/or cell death.15 High levels of MnSOD with decreased catalase may create an antiapoptotic intracellular environment which is especially susceptible to increased frequencies of mutation, a situation likely to lead to cell transformation and cancer.16 These findings suggest that the disturbance in oxidant-antioxidant balance may promote gastric carcinogenesis.