CAT and cancer: These results can potentially provide two interesting scenarios regarding Trx, cancer and aging: 1) overexpressing Trx in the mitochondria could play a more important role on lifespan than in the cytosol, which is similar to the results of the mCAT mice studies (overexpressing catalase in the mitochondria increased lifespan, but overexpressing catalase in the nucleus or the cytosol had no effect); and 2) down-regulating Trx in the cytosol could play important roles in suppressing cancer development, which may have beneficial effects in older animals.