Elevated levels of serum leptin and overexpression of leptin receptors are associated with RCC invasion and progression, and activation of the extracellular signal-regulated kinases (ERK1/2) and janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3) signaling pathways participates in leptin-mediated proliferation of RCC Caki-2 cells [69-71]. Here, STAT3 is linked to renal cell carcinoma.