Molecular heterogeneity of variant Philadelphia translocations in childhood acute lymphoblastic leukaemia

In acute lymphoblastic leukemia (ALL), it is unclear whether variant Philadelphia (Ph) translocations have the same molecular and clinical implications as the classical translocation. Two children with Ph+ ALL with variant translocations are described. One, in whom cytogenetic remission was not achieved, had evidence of translocation of c-abl to chromosome 22, rearrangement of minor breakpoint cluster region (mBCR) and expression of hybrid bcr/abl transcripts. In the other case, no gene rearrangement was found and complete remission was achieved. Variant Ph translocations in childhood ALL are heterogeneous at the molecular level. Molecular studies coupled with observations of clinical outcome are needed in larger numbers of such children to determine whether poor clinical response correlates with bcr/abl involvement and to allow planning of appropriate therapeutic strategies.