Mechanistic studies identified multiple sources of ROS production in cancer cells, such as increased expression and activity of the enzymes NADPH oxidase 1 and 4 (NOX1, NOX4) and cyclooxygenase-2 (Cox-2), transcriptional repression of sestrin family genes, and increased ROS production by the cytochrome c-oxidoreductase in the mitochondrial electron transport chain[52-59] [Figure 2]. Here, PTGS2 is linked to cancer.