CAT and neoplasm: This study is based on the working hypothesis that the established reactivation of extracellular NO/peroxynitrite and HOCl signaling of tumor cells after reactivation of membrane-associated catalase is not necessarily sufficient for the induction of apoptosis, as it may be counteracted by the interaction of intracellular glutathione and glutathione peroxidase, which counteract the effects of the ROS/RNS signaling on the membrane.