When administered to irradiated tissue, melatonin boosted SOD2 activity in normal tissue but not cancer tissue.35 The hypothalamic–pituitary–adrenal gland axis has a stress-induced increase of cortisol levels that can cross the BBB, which can also induce ROS and OS and reduce the expression of melatonin, which may affect SOD2 activity. Here, SOD2 is linked to cancer.