FMO5 and cancer: The role of ROS-dependent NADPH oxidase in biological systems can be classified into at least two functions: (1) promoting oxidative stress; an imbalance between the generation and neutralization of ROS in cells has deleterious effects on macromolecules, such as proteins, nucleic acids and lipids, leading to cellular damage and enhancing the risk of mutations; and (2) the regulation of several signaling pathways that are redox sensitive contributes to cancer pathophysiology [59,60].