HDAC9 and cancer: Here, based on the transcriptomic, genomic, and clinical data from the TCGA database [24], Prognoscan platform [26], and TIGER database [39], and using several other bioinformatic tools [31,35,36,39,40,41], we demonstrated that the expression levels of class I and class II HDAC genes are related to cancer stemness and immunity, however, in a distinct manner.