HDAC9 and cancer: HDACs are either Zn2+ (classes I, II, and IV) or nicotinamide adenine dinucleotide-dependent (class III) [5], and while the contributions of specific HDAC subtypes to individual cancers have not been fully elucidated [5,6], HDAC inhibitor (HDI) candidates, for instance, suberoylanilide hydroxamic acid (SAHA, also known as vorinostat), can interfere with cancer progression.