In the framework of the development of leukaemia, in addition to high levels of reactive oxygen species (ROS), the expression and activation of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxides (GPx) are disturbed, in particular, both SOD and CAT activity are reduced in lymphocytes from ALL and CLL patients [137, 138]. Here, CAT is linked to B-cell chronic lymphocytic leukemia.