Acute lymphoblastic leukemia with a late- appearing Philadelphia chromosome: case report and review of the literature.

UNLABELLED We describe a rare presentation of acute lymphoblastic leukemia in a young adult male who at the beginning of the disease lacked the Philadelphia chromosome in bone marrow and blood cells and fluorescence in situ hybridization was negative for the presence of a clone with the BCR-ABL1 rearrangement. The patient initially had pancytopenia with a blast cell count of 5% in the peripheral blood that evolved to a phase with progressive leukocytosis and a sudden rise in blast cells 7 months later. At this time, his bone marrow aspirate showed the presence of a neartriploid karyotype containing two Philadelphia chromosomes. The multiple karyotypic changes observed in our patient support the notion that leukemic progression involves several cytogenetic evolutionary processes, the first step of which may not necessarily involve acquisition of the Philadelphia chromosome. KEYWORDS Late-appearing Philadelphia chromosome, adolescent ALL, BCR-ABL1, dasarinib.