For example, glutathione is overexpressed in cancer cells (up to 10 × 10−3 m), which is an important pathway to protect cells from oxidative damage by ROS scavenging.[[qv: 7]] Moreover, another important representative phenomenon is the production of excessive content of catalase (CAT).[[qv: 8]] CAT is an essential antioxidant enzyme in cells, which plays a crucial role in maintaining the balance of intracellular ROS by decomposition of H2O2 and decreasing highly toxic ·OH production by intracellular iron through H2O2. Here, CAT is linked to cancer.