SOD1 and cancer: Cancer cells have an elevated metabolism and higher levels of ROS than normal cells, but normally they maintain ROS at acceptable levels with an excellent antioxidant system including NRF2 transcription factor, the main regulator of intracellular redox homeostasis, and the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) [53].