In fact, when HDAC inhibitors are combined with other inhibitors, including blockers of DNA methyl transferases, it was reported that the combination increased antitumor effects on myelodysplastic syndrome and prostate, ovarian, and pancreatic endocrine tumor cells, suggesting superior benefits for carefully selected combinations including HDAC inhibitors [13]. Here, HDAC9 is linked to pancreatic neuroendocrine tumor.