HDAC9 and esophageal cancer: 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.