[Cytogenetic and clinical features of Philadelphia chromosome positive leukemias].

The Philadelphia chromosome defines chronic myeloid leukemia, and is mostly based on a translocation t(9;22) with a typical BCR-ABL rearrangement which also occurs in so called atypical translocations. The transformation of chronic myeloid leukemia is associated with clonal evolution in 80% of cases. The appearance of an isochromosome 17q unequivocally heralds the onset of a myeloid type of blast crisis. Treatment of Ph-positive CML has still to be considered palliative except for allogeneic bone marrow transplantation. The Philadelphia chromosome is also found in about 20% of patients with acute lymphoblastic leukemia and in about 2% of patients with nonlymphoblastic leukemia. It is associated with a poor prognosis. Molecular and cytogenetic findings help differentiating between de novo acute leukemia and blast crisis of chronic myeloid leukemia.