FMO5 and cancer: Recent studies have shown that high levels of ROS in cancer cells are the result of increased basal metabolic activity, mitochondrial dysfunction, due to hypoxia or mitophagy, peroxisomes activity, uncontrolled growth factors of cytokine signaling, oncogene activity, as well as enhanced activity of known ROS sources, such as NADPH oxidase, cyclooxygenases, or lipoxygenases (132–134) in cancer cells.