APEX1 and cancer: Human APE1 is genetically altered and aberrantly expressed and localized in cancer patients and has become an emerging therapeutic target for various cancer therapy (Abbotts and Madhusudan, 2010; Al-Safi et al., 2012; Fishel and Kelley, 2007; Koukourakis et al., 2001; Sengupta et al., 2016; Thakur et al., 2014; Yoo et al., 2008).