RRM2B and esophageal squamous cell carcinoma: Recent fundamental research indicated that many biological markers associated with apoptosis, DNA repair and the cell cycle such as tumor suppressors (p53, p21), cell-cycle regulators (cyclin D1, CDC25B, 14-3-3 sigma), DNA repair (p53R2, ERCC1) are associated with response to CRT in esophageal squamous cell carcinoma (ESCC) [5-7].