MLL cleavage occurs in approximately 5% of de novo acute myeloid leukemia, including in patients analyzed before treatment induction.

To the Editor: Aplan et al[1][1] recently reported a site-specific DNA cleavage induced by topoisomerase II (Topo II) inhibitors within the MLL gene breakpoint cluster region on chromosome 11q23. The finding was initially identified by Southern blot analysis of circulating blasts taken from a case