Extramedullary disease in acute promyelocytic leukemia.

All-trans retinoic acid (ATRA) is currently recommended as standard treatment for acute promyelocytic leukemia (APL). However there has been increasing concern that ATRA is associated with unusual sites of relapse. Although there is insufficient evidence so far to substantiate this, we review the potential mechanisms by which ATRA may increase the incidence of extramedullary and, in particular, central nervous system (CNS) relapse.