Universal and Specific Functions of STAT3in Solid Tumours

STAT3 is constitutively activated in a high percentage of tumours and tumourderived cells of both liquid and solid origin, often correlating with aggressive disease and bad prognosis. Persistent STAT3 activity, to which tumours often become addicted, is mostly due to the aberrant activation of pro-oncogenic/proinflammatory signals that can trigger its phosphorylation, such as oncogenes, growth factor receptors and cytokines. Among STAT3-mediated functions are increased survival and proliferation, enhanced angiogenesis, motility and invasion, and down-modulation of anti-tumour immune responses. Moreover, STAT3 was recently shown to play unexpected roles in regulating cell metabolism and mitochondrial activity via both transcriptional and non-transcriptional mechanisms. Here, we review the main knowledge about the role of STAT3 in solid tumours, with a particular focus on breast cancer and our recent work with mouse models.