A Ph-negative Chronic Myeloid Leukemia Patient with a Non-classical BCR-ABL Rearrangement Characterized by Fluorescence In Situ Hybridization

A patient with chronic myeloid leukemia (CML), a normal karyotype and a BCR-ABL rearrangement is presented. Southern blot analysis detected the rearrangement, whereas RT-PCR with b2a2 and b3a2 primers did not. Fluorescence in situ hybridization (FISH) with an ABL probe (9q34.2) and an Mbcr probe (22q11) showed ABL and BCR signals on chromosome 22. Subsequent FISH studies with cosmids mapping to 9q34.3 showed normal hybridization patterns to chromosome 9, suggesting an interstitial insertion of ABL containing DNA sequences into chromosome 22 in this patient. The lack of reciprocal translocation sequences was investigated with RT-PCR, primers a1b and c7. The absence of ABL-BCR gene expression in this and other patients described in the literature with this subtype of Ph-negative CML, does not seem to have an impact on the clinical course of the disease.