KMT2A (MLL)-MLLT1 rearrangement in blastic plasmacytoid dendritic cell neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy characterized by CD4 and CD56 coexpression without apparent lineage commitment. The molecular pathogenesis of BPDCN has been studied in only a limited number of cases, and specific chromosomal aberrations are lacking thus far. KMT2A (MLL) rearrangements are observed in various types of pediatric and adult leukemia, but only one adult case report has so far showed KMT2A (MLL)-MLLT1 gene rearrangements in BPDCN. We present the first pediatric case of BPDCN with a KMT2A (MLL)-MLLT1 rearrangement confirmed by molecular study. The karyotype demonstrated a t(11;19)(q23;p13.3), trisomy 8, and trisomy 19 in all 20 metaphase cells analyzed: 48,XX,+8,t(11;19)(q23;p13.3),+19[20]. Fluorescence in situ hybridization analysis showed KMT2A (MLL) gene rearrangement in 83% of interphase cells. The KMT2A (MLL)-MLLT1 gene rearrangement was confirmed by multiplex reverse transcriptase polymerase chain reaction. We suggest that the pathogenesis of BPDCN could be associated with KMT2A (MLL) rearrangement (especially with KMT2A (MLL)-MLLT1) and further study on a larger number of cases is needed.