STAT3 and cancer: Interestingly, the tumor suppressor activity of two further PTPs has recently been linked to STAT3 inactivation: PTPRD was found frequently inactivated and unable to dephosphorylate the oncoprotein STAT3 in glioblastoma and in other human cancers and PTPRT was shown to reduce IL-6 mediated STAT3 activation in HCT116 cell lines [27,28].