Biphenotypic acute leukemia (BAL) is a rare type of leukemia, comprises 4% of all acute leukemias. It is more common in adults and the clinical features, as related to marrow dysfunction, are similar to those found in other patients with acute leukemia. BAL commonly shows a dimorphic blast population with, one resembling lymphoblasts and the other resembling myeloblasts. The majority of BAL patients express B-lymphoid and myeloid markers. BAL can be diagnosed by morphologic studies and by a comprehensive panel of immunological markers, as well as cytogenetic/molecular studies, such as fluorescence in situ hybridization (FISH) and reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, its prognosis is relatively poor. We present here a 27 year-old female patient who showed lymphoblasts and myeloblasts on her marrow studies and these cells were positive for myeloid and B-lymphoid markers on the immunophenotypic studies. Chromosome analysis revealed 46,XX,t(6;19)(p23;p13.1),t(9;22)(q34;q11.2). A major (b3a2) type of BCR-ABL1 mRNA transcript was detected by RT-PCR, and a 5'ABL1 deletion was identified by FISH. (Korean J Hematol 2009;44:249-254.)

Keywords: Biphenotypic acute leukemia (BAL), t(9,22)(q34,q11.2), BCR-ABL1 mRNA transcript, 5'ABL1 deletion