The potential clinical utility of the use of DACi in cancer therapy was first suggested by the activity of the DACi, sodium phenylbutyrate, against acute promyelocytic leukemia (APL). An adolescent female patient with relapsed APL, who no longer responded to all trans-retinoic acid (ATRA) alone, achieved a complete clinical remission after treatment with a combination of ATRA and the DACi sodium phenylbutyrate.