In esophageal cancer, high expression of HDAC1 was detected in ESCC samples especially in the carcinoma invaded into the deeper layers of the esophageal wall.18 Application of Valproic acid, a class I HDAC inhibitor, enhanced sensitivity of ESCC cells toward radiotherapy.19 The expression and function of HDAC6 in esophageal cancer has not been studied yet. This evidence concerns the gene HDAC9 and esophageal squamous cell carcinoma.