Fish analysis at diagnosis in acute lymphoblastic leukemia

Many recurrent cytogenetic abnormalities have been described in acute lymphoblastic leukemia (ALL). With improvement of survival, it became evident that some of these chromosomal changes had a major prognostic value: hyperdiploidy and t(12;21) are associated with very long disease free survival, whereas t(9;22) and 11q23 rearrangements correlate with a poor outcome. Because of this prognostic impact, detection of these four specific abnormalities has to be accurate and rapid at diagnosis. In order to reliably analyze ALL patients, we used fluorescence in situ hybridization (FISH). We selected specific probes enabling the detection of the structural rearrangements [t(9;22), t(12;21) and 11q23 rearrangements] directly on interphase cells. Detection of hyperdiploidy was performed using comparative genomic hybridization (CGH). This technique enables to characterize chromosomal gains and losses without requiring metaphase obtention. We showed that this FISH-based approach was complementary to conventional cytogenetics, and should be systematically used in ALL at diagnosis.