One of the mechanisms through which leptin causes breast cancer progression is the regulation of breast cancer stem cell (CSC) activity by modulating the many signalling pathways (i.e., Notch, Wnt, mTOR, STAT3, HER2/Erb, and IGF pathways) and transcription factors (i.e., HIF-1 and NFκB) [65,66,67,68,69]. The gene discussed is STAT3; the disease is breast carcinoma.