CBFB/MYHII fusion in a patient with AML-M4Eo and cytogenetically normal chromosomes 16

We present a unique case of acute myeloid leukemia M4Eo (AML-M4Eo) with a C BFB/MYH11 fusion transcript and a trisomy 22, but in whom cytogenetic analy ses did not disclose an inv(16). Fluorescence in situ hybridization (FISH) analysis with chromosome arm-specific painting probes as well as with the c 40 and c36 cosmids also revealed no evidence for an inv(16), whereas the ap plication of locus-specific probes confirmed the presence of a masked inv(1 6). The results of our comprehensive FISH investigations indicate that the events leading to this masked inv(16) were complex and concurred with delet ions on both the long and short arms. The most likely explanation for the f ormation of the relevant CBFB/MYH11 fusion is an insertion of parts of the MYH11 into the CBFB gene, although it is also possible that it was formed b y a double inversion. (C) 2000 Wiley-Liss, Inc.