Vorinostat (SAHA: suberoylanilide hydroxamic acid) was the first HDAC inhibitor to be approved for clinical use by the FDA for the treatment of refractory cutaneous T-cell lymphoma.8 In several clinical trials, vorinostat was active against leukemia and lymphoma, but rather modestly effective against solid tumors.9 As HDACs are involved in numerous essential cellular processes, the clinical use of broad-spectrum HDAC inhibitors is associated with dose-limiting side effects such as thrombocytopenia, fatigue, nausea, diarrhea and anorexia (reviewed in Lane and Chabner9and Witt et al.10). Here, HDAC9 is linked to leukemia.