Tumour proliferation promoted by leptin involves the activation of the extracellular signal-regulated kinases (ERK1/2) and Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3) signalling pathway, as well as the upregulation of vascular endothelial growth factor (VEGF) via hypoxia-inducible factor-1α (HIF-1α) and nuclear factor-kappa B (NF-κB), which results in apoptosis inhibition and enhanced cancer cell proliferation [30,32,33,35]. The gene discussed is STAT3; the disease is cancer.