Deletions of the 3′ BCR and 5′ ABL regions in patients with Philadelphia-positive chronic myeloid leukemia: a one-step process occurring in about 10% of the cases without any evidence of genetic instability in the target cells

Deletions of the 5′ ABL region adjacent to the t(9;22)(q34;q11) have recently been reported in 8–32.7% of patients with chronic myeloid leukemia (CML). The deletions were visualized with fluorescence in situ hybridization using, in the majority of the cases, the Vysis LSI BCR/ABL ES (extra signal) probe. In our series, 10 of 99 CML patients (10.1%) were characterized by a 5′ ABL deletion. We show that 3′ BCR losses are observed in nearly all the cases with 5′ ABL deletions. Moreover, the different genetic events (Philadelphia chromosome formation; 5′ ABL and 3′ BCR deletions) occur simultaneously in a one-step process without any evidence for genetic instability in the target bone marrow cells.