While atRA inhibited LSC activity in FLT3-ITD bearing non-APL AML, the opposite was reported for AML expressing the AML1-ETO fusion or overexpressing EVI1. atRA strongly increased the serial replating ability of AML1-ETO expressing murine BM cells, and resulted in larger, more immature colonies [9]. Here, MECOM is linked to acute promyelocytic leukemia.