HDAC9 and cancer: Only a few studies have evaluated the level of class I HDAC expression in cancer: Huang BH et al. [28] demonstrated that HDAC1 and HDAC2 seem to be upregulated in colon cancer; Choi JH et al. [29] demonstrated an overexpression of HDAC1 mRNA 68% of gastric cancer tissues studied by them (17 of 25) and elevated expression of HDAC1 protein was also detected in 61% of the gastric cancer samples (11 of 18).