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Chronic lymphocytic leukemia (CLL) is a heterogeneous disease, with variable clinical presentation and evolution. Two major subtypes can be distinguished, mutated (M) and unmutated (UM), characterized respectively by a high or low number of somatic hypermutations in the variable region of immunoglobulin genes and different outcome. Cytogenetic and FISH (fluorescence in situ hybridization) studies have proved to be important tools in the biologic characterization of this disease, allowing the identification of distinct risk groups. Genomic instability involves a process prone to the accumulation of chromosome alteration in somatic cells and is a major driving force of tumorigenesis. The analysis of chromosome aberrations (CA) and micronucleus (MN) represent different forms to evaluate genomic instability.

In this study, we have analyzed the basal frequency of CA and MN in untreated CLL patients. Results were evaluated in relation to different prognostic factors.

A total of 67 untreated CLL patients (36 males; mean age: 66.6 years; range: 42-83 years; Rai stage: 0: 27%; I-II: 59%; III-IV: 14%), and 6 normal controls, were studied. Chromosome analysis was performed on stimulated peripheral blood lymphocytes cultures. For each patient, CAs were evaluated on 50 cells stained with 10% Giemsa and the MN frequency was assessed on 250 interphase nuclei. FISH analysis was performed using the CLL panel according to manufacturer´s protocol. IGHV (immunoglobulin heavy chain variable region) mutational status was analyzed by RT-PCR and bi-directional sequencing. The study was approved by the local Ethics Committee. All individuals provided their informed written consent.

An increased number of CAs, including chromatid breaks and dicentrics, in CLL patients (6.59±5.3%) compared to controls (0.25±0.04%) (p=0.021) was observed. A tendency to increased CA frequency in cases with abnormal (8.18±6.1%) compared to normal karyotypes (5.67±4.4%) (p=0.08) was also found. The analysis taking into account FISH risk groups showed a higher frequency of CA in patients with deletions 11q22 and/or 17p13 associated to poor outcome (8.54±6.1%), than those with no alterations or 13q14 deletion related to a better outcome (5.64±3.9%) and cases with +12 with an intermediate prognosis (4.54±3.5%). By MN analysis, an increased frequency in CLL patients (2.81±1.5%) compared to controls (0.67±0.3%) (p=0.0001) was found. Patients with +12 presented the highest percentage of MN compared to the other two groups (~1.3-fold), indicating the aneugenic effect of this alteration. The evaluation according to the IGHV mutational status showed similar frequencies for CAs and MN in M-CLL (6.2±5.2% and 2.82±4.9%, respectively) and UM-CLL (6.2±5.8% and 2.7±1.3%, respectively). No association between CA and MN frequencies and clinical parameters was found.

Our results confirm the presence of basal genomic instability in untreated CLL patients as measured by both CA and MN techniques. To our knowledge, this is the first analysis of these parameters taking into account prognostic factors of the disease. Cases with deletions 11q22 and/or 17p13 had the highest value of CA and those with +12 showed the highest frequency of MN, reflecting different mechanism of DNA damage.