ER is characterized by direct antioxidant activity, because it is able to react with hydrogen peroxide and alkylhydroperoxides to form water and an alcohol [30,50], but also by indirect antioxidant capacity, being a potent inducer of cellular antioxidant systems, like the thioredoxin reductase 1 (TrxR1), as demonstrated in human breast cancer MCF-7 cells [60]. The gene discussed is TXNRD1; the disease is breast cancer.