A PH(-LEUKEMIA EXPRESSING BOTH CML-TYPE AND ALL-TYPE BCR() ACUTE MYELOID)ABL MESSENGER-RNA TRANSCRIPTS/

This report describes a patient presenting with acute myeloid leukaemi a (AML-FAB classification M2). Phenotypic markers were positive for ce lls of the myeloid lineage, but negative for monocyte/macrophage, mega karyocyte, and T-cell lineages. The occasional blast was positive for CALLA. All blasts carried the Philadelphia chromosome (Ph(+)), with 20 % also harbouring a monosomy 7 (a cytogenetic marker for AML). Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed th e presence of two BCR/Abl mRNA transcripts; b(2)a(2), the Chit-type an d E(1)a(2), the ALL-type. Immunoglobulin (Ig) gene analysis demonstrat ed the presence of a small population of cells containing rearranged I g genes. After a short remission, the patient relapsed. At relapse the leukaemia had undergone a major phenotypic switch from AML to ALL, wi th blasts bearing B-cell markers. Ig gene analysis confirmed a monoclo nal population of B-cells. The Ph(+); persisted, but the monosomy 7 ha d disappeared. The same two BCR/Abl mRNA transcripts were found at rel apse as at presentation. To our knowledge, this is the first report of an AML simultaneously expressing BCR/Abl transcripts from both the mi nor and major BCR. The possible mechanisms of this dual expression are discussed.