LEP and neoplasm: Leptin binds to leptin receptors to activate the Janus kinase/signal transducer and activator of transcription (JAK/STAT), mitogen-activated protein kinase/extractor signal regulated kinase (MAPK/ERK) and phosphoinositide-3 kinase/protein kinase B (PI3K/AKT) (17–19), and the expression of multiple genes in these signaling pathways promotes the proliferation and metastasis of tumor cells (Figure 2).