STAT3 and cancer: One of the most well-defined regulatory circuits linking chronic inflammation and cancer is formed by two distinct but complimentary feedback regulatory loops involving either IL-6, NF-κB, and Lin28, let-7 miRNA or IL-6, NF-κB, STAT3, miR-21, miR-181b-1, and the tumor suppressor genes PTEN and CYLD [41,44].