JAK2 and breast cancer: Specifically, leptin is thought to promote breast cancer through the activation of Janus kinase 2/Signal Transducers and Activators of Transcription 3 (Jak2/Stat3), mitogen-activated protein kinase (MAPK) and Phosphatidylinositol-3-kinase/Protein kinase B (PI3K-AKT) [13].