STAT3 in cancer: A double edged sword.

•STAT3 can behave both as an oncogene and an oncosuppressor.•Activation by many signals and heterogeneous target genes can explain this feature.•Specific post-translational modifications dictate different cellular localization.•These activities contribute to regulate energy metabolism and autophagy.•Finally, STAT3 controls the properties of both the tumor and its microenvironment.