HDAC9 and acute promyelocytic leukemia: It has been shown for instance that the resistance to all-trans retinoic acid (ATRA) observed in acute promyelocytic leukemia (APL) cells carrying the variant PLZF-RARA fusion protein may be abrogated by HDAC inhibitors (HDACi) such as trichostatin A or sodium phenylbutyrate in vitro or in vivo [10-11].