It is produced in the mitochondria, mainly through the activationof the nicotinamide adenine phosphate dinucleotide oxidase complex(NADPH),514 which is an important signalingmolecule for cell growth, proliferation, and differentiation.515 Increased concentrations of H2O2 at tumor sites are closely related to tumor cell growth,development, and apoptosis. The gene discussed is DECR1; the disease is neoplasm.