STAT3 and neoplasm: PTPRK dephosphorylates and inactivates oncogenic proteins such as STAT3, EGFR and CD133, is frequently downregulated in human cancers, and is considered a tumor suppressor (McArdle et al., 2001; Flavell et al., 2008; Tarcic et al., 2009; Assem et al., 2012; Scrima et al., 2012; Mo et al., 2013; Sun et al., 2013; Chen et al., 2015; Shimozato et al., 2015).