Evidence of myeloid differentiation in non-M3 acute myeloid leukemia treated with the retinoid X receptor agonist bexarotene

All-trans-retinoic acid has dramatically changed the treatment paradigm for acute promyelocytic leukemia, however, it has no significant activity in non-M3 acute myeloid leukemia (AML). In vitro, bexarotene, a retinoid X receptor agonist inhibits the proliferation of non-M3 AML cell lines and induces differentiation of leukemic blasts from patients. We hypothesized that there may be similar activity in patients with AML. We report on two patients with relapsed or refractory non-M3 AML treated with bexarotene monotherapy. After initiating treatment, both patients showed leukemic differentiation in their peripheral blood and reduction in bone marrow blasts to less than 5%. One patient had a significant improvement in her platelet count with loss of platelet transfusion needs. Differentiation syndrome occurred in one patient and was successfully treated with steroids and discontinuation of bexarotene. These data suggest that bexarotene has clinical activity in non-M3 AML and may be able to induce myeloid differentiation in vivo.