STAT3 and cancer: Multiple negative regulators, such as SOCS3, SHP-1 and PIAS, have crucial roles to keep STAT3 activity at low levels in normal conditions.6, 7, 8, 9 However, constitutive activation of STAT3 is frequently observed in tumor cells and is considered as ‘oncogenic’.10, 11, 12, 13 Clinically, the upregulation of STAT3 in cancer cells is linked with a worse prognosis, severer drug resistance and shorter survival period in patients.14, 15