Importantly, it has been reported that HDAC1 and HDAC2 play essential and redundant roles in leukemia cell survival and proliferation, establishing the plausibility that HDAC inhibitors selective for these two isozymes might retain anti-leukemic activity while obviating toxicity associated with inhibition of other HDACs, such as HDAC3 [22, 23, 47, 48, 75]. Here, HDAC9 is linked to leukemia.