Detection of cryptic MLL insertions using a commercial dual-color fluorescence in situ hybridization probe

Involvement of the MLL gene located at chromosome region 11q23 is a frequent occurrence in both acute myelocytic leukemia and acute lymphoblastic leukemia. More than 30 loci have now been associated with MLL, usually by reciprocal translocation. Deletions, insertions, and more complex rearrangements of MLL are rarely seen. We present three cases of AML M5 showing no cytogenetic evidence of 11q23 rearrangement, in which a commercial MLL dual-color fluorescence in situ hybrdization probe revealed a nonstandard abnormal signal pattern, suggesting cryptic insertion of the MLL gene into its partner gene site.