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The diagnostic hallmark of chronic myelogeneous leukemia (CML), the Philadelphia (Ph) translocation, has been proven to be most important for diagnosis and monitoring of the disease. The Ph-translocation leads to fusion of the ABL gene located on 9q34 to the BCR gene on 22q11. Its partial or complete disappearance is correlated to the clinical outcome. Fluorescence in situ hybridization (FISH) has been proven to be a helpful technique in diagnosis and monitoring of BCR-ABL gene fusion. A minority of of patients with CML had large deletions adjacent to the translocation breakpoint on the derivative chromosome 9, on the additional partner chromosome in variant translocations, or on both. Several studies have shown those cases to have a poorer outcome than cases with only the Ph-translocation. To assess the extent of the deletion of chromosome 9 and 22 sequences, we performed microarray-based comparative genomic hybridization (array-CGH) on a platform with 6935 clones on five Ph-positive cases of CML. The deletion on 9q have been detected beforehand with a BCR-ABL FISH probe (fluorescence in situ hybridization) in bone marrow samples of these patients (Table 1). The lengths of the deletions vary between 747.035 bps and 3.587.395 bps (Table 1). A trisomy 21 and additional Ph-chromosome were confirmed. New submicroscopic gains and losses were also detected. We here present the first study on array CGH used to characterize the lengths of the deletion of chromosome 9 and 22 sequences in Ph positive CML. The length of the deletion seems not to influence the clinical course of the disease within this subgroup of patients. These data represent just a tendency, since only five cases have been investigated in this pilot study. A study with a larger number of cases is needed to confirm this assumption. Table 1. Correlation between FISH patterns used to detect the deletions and lengths of the deletions on 9q and 22q detected with array CGH *Patterns are observed with the LSI BCR/ABL Dual Color Dual Fusion (D-FISH) probe; f: fusion (#Ph); r: red (#9); g: green (#22)

[Proc Amer Assoc Cancer Res, Volume 46, 2005]