Acquired chromosomal rearrangements targeting selected transcription factors: contribution of molecular cytogenetic and expression analyses to the identification of clinically and biologically relevant subgroups in hematological malignancies.

In leukemias chromosomal aberrations, balanced translocations in particular, play a critical role in the oncogenic process. The characterization of these chromosomal alterations was crucial to the discovery of the genes implicated in leukemogenesis, as the chromosomal breakpoints indicated their genomic localization. In addition, these molecular defects may serve as targets for diagnostic essays and can have a major prognostic value. Finally, the characterization of the deregulated cellular pathways potentially identifies targets for therapeutic intervention. In this paper we summarize our efforts to expand the current knowledge of the diagnostic, prognostic or biological significance of selected chromosomal aberrations identified in M-FISH studies. First, we illustrated the power of M-FISH in dissecting complex chromosomal aberrations in myeloid neoplasms. MLL amplification was defined as a clinical entity characterized by adverse prognosis and within the multitude and variety of chromosomal rearrangements a pattern of a limited number of cytogenetic subclasses was discerned. In leukemias characterized by 11q23 amplification, we described the amplicon and confirmed MLL, in addition to DDX6, as a principal amplification target. Molecular characterization of a large series of unselected sporadic and recurrent 3q26 rearranged leukemias confirmed the decisive role of ectopic EVI1 expression in these malignancies. We contributed to an extensive analysis of the phenotypical and prognostic features of T-ALL characterized by HOX11L2 expression and identified HOX11L2 overexpression as one of the most frequent genetic defects in childhood T-ALL, associated with intermediate prognosis. Finally, we designed and validated diagnostic tools for the detection of the t(9;14) (p13;q34) resulting in PAX5 overexpression and convincingly associated the presence of this rearrangement to high-grade morphology and karyotype complexity. In conclusion, the series of investigations presented here clearly illustrate the benefits of M-FISH as molecular tool for the dissection and characterization of complex and cryptic rearrangements. The subsequent reports demonstrate the utility of molecular cytogenetics and expression analyses to the clinical management of patients diagnosed with hematological malignancies.