STAT3 and breast cancer: In line with these observations, a growing body of evidence have shown that leptin is able to induce a variety of responses, such as mitogenesis, survival, transformation, migration and invasion in breast cancer cells 13–20 through the activation of several signalling pathways, such as those involving Janus kinase 2–signal transducer and activator of transcription 3 (JAK2-STAT3), mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3-kinase-protein kinase B (PI3K-AKT) 21.