An overview of translocation-related oncogenesis in the chronic myeloid leukaemias.

The demonstration of the BCR-ABL fusion gene in patients with chronic granulocytic leukaemia and t(9;22)(q34;q11) represents the first recognition, in a human neoplasm, of a translocation leading to formation of an oncogenic fusion gene. Since this initial observation, this leukaemogenic mechanism has been increasingly recognized in chronic myeloid leukaemias. The fusion gene has often incorporated part of a gene encoding a receptor or cytoplasmic tyrosine kinase, particularly ABL, PDGFRB and FGFR1. This contrasts with the frequent involvement of genes encoding transcription factors or other nuclear proteins in acute myeloid leukaemia. Nevertheless, genes encoding tyrosine kinases have also been implicated in some cases of acute leukaemia. With the exception of the BCR-ABL fusion gene in chronic granulocytic leukaemia, all these fusion genes are uncommon or rare among cases of chronic myeloid leukaemia. The molecular mechanisms underlying the great majority of cases of Philadelphia-negative chronic myeloid leukaemia remain to be discovered.