Apurinic apyrimidinic endonuclease 1/Redox factor-1 (APE1/Ref-1) is a multifunctional protein; its N-terminal region is involved in redox activity and regulates multiple transcription factors, and its C-terminus is involved in base excision DNA repair activity. APE1/Ref-1 is mainly localized in the nucleus and shows dynamic shuttling between the nucleus and cytoplasm in response to various stress stimuli. Recently, it have a reported the possibility for the extracellular secretion of APE1/Ref-1. Elevated level of APE1/Ref-1 were observed in the blood of endotoxemic rats, and in bladder cancer.