A small pool of acetylated and Ser727-phosphorylated STAT3 is localized to mitochondria, where it may promote malignant transformation and cancer progression by supporting the optimal function of mitochondrial electron transport chain and inhibiting the production of reactive oxygen species.30–32 Furthermore, association of cytoplasmic STAT3 with a mictotublule-destabilizing protein stathmin potentiates microtubule polymerization and cell movement.33 Thus, transcriptional and cytoplasmic activities of STAT3 may function in concert to promote tumorigenesis. This evidence concerns the gene STAT3 and cancer.