Cytogenetics of chronic myeloid leukaemia

The standard Philadelphia (Ph) translocation t(9;22), its variants and a pr oportion of Ph-negative cases are positive for the BCR-ABL fusion gene, as determined by molecular analysis. Extensive deletions of chromosome 9 and 2 2 derived sequences around the translocation breakpoints on the derivative 9 are seen in 10-30% of patients at diagnosis and may confer a worse progno sis. Additional cytogenetic changes can occur in the few months before or d uring disease progression and are often specific for blast morphology; howe ver, the molecular basis of the most common additional cytogenetic abnormal ities is largely unknown. Cytogenetics is important for monitoring patient response to treatment but is increasingly being replaced by the more sensit ive and less invasive techniques of RT-PCR and FISH.