HDAC9 and malignant endocrine neoplasm: Histone deacetylase (HDAC) activity is indispensable for EZH2-mediated gene repression [48], and HDAC inhibitors can induce NOTCH1 expression in some endocrine cancers [49], indicating the relevance of EZH2 and NOTCH1 and their convergence at HDAC.