However, a complete understanding of the sources of tumor cell ROS has only recently begun to be developed, having awaited the discovery over the past decade of the family of six epithelial NADPH oxidases (Noxs) that have significant homology with the membrane oxidase of leukocytes (5), and the development of reagents that allow evaluation of expression of the members of the Nox gene family across different tissues and tumors. This evidence concerns the gene FMO5 and neoplasm.