STAT3 and esophageal squamous cell carcinoma: In esophageal squamous cell carcinoma, IL-6 derived from cancer-associated fibroblasts plays the most important role in chemoresistance by upregulating the expression of C-X-C motif chemokine receptor 7 (CXCR7) via the STAT3/nuclear factor-κB (NF-kB) pathway (53).