HDAC9 and acute promyelocytic leukemia: Thus, HDAC play an important role in APL, however their role varies over time as HDAC1/2 knockdown in early leukemogenesis expands the leukemia, whereas in leukemic phase, knockdown of the same HDAC1/2 cause differentiation and apoptosis of APL cells, and increased survival of APL mice [36].