Chromosome Aberrations by Conventional Karyotyping in Chronic Lymphocytic Leukemia Carrying No Aberration by Fluorescence in Situ Hybridization: Correlation with Prognostic Parameters and Clinical Features

Abstract 1459

Background. Chronic lymphocytic leukemia (CLL) is a clinically heterogeneous disease. Adverse prognostic parameters include stage, CD38 and/or ZAP70 expression, the unmutated configuration of the variable region of the Ig heavy chain gene (IGHV) and the presence of specific chromosome aberrations. Using fluorescence in situ hybridization (FISH) with probes detecting trisomy 12 and deletions at 13q14, 11q22–23/ATM and 17p13/p53, approximately 60–80% of the cases carry an abnormality. Patients without FISH aberrations (“normal” FISH) have a relatively favourable outcome. Improved mitotic stimulation using oligonucleotide (odn) and interleukin-2 (IL-2) can detect karyotype aberrations in chromosome regions not covered by the classical 4-probe panel. This study was designed to assess whether the presence of karyotypic aberrations in CLL patients with “normal” FISH may have a correlation with established clinical and prognostic parameters.

Methods. Eighty-four patients with “normal” FISH results referred to our laboratory between 2007 and June 2011 were included in the present report. These patients represent consecutive CLL cases diagnosed and treated, according to the NCI criteria, at 4 GIMEMA CLL group centres between 2006 and 2011. Indications for treatment included advanced stage (Binet C) or disease progression. The Matutes immunophenotypic score was calculated giving 1 point to CD5+, CD23+, CD22weak+, sIg weak+ and FMC7- and only patients with a score ≥3 (i.e. typical CLL) were included. The coexpression of the CD38 and CD19 antigens and ZAP-70 was tested on fresh PB cells with a 20% cut-off for positivity. IGVH genes were amplified from genomic DNA and sequenced according to standard methods and the cut-off of 98% homology to the germline sequence was chosen to discriminate between mutated (<98% homology) and unmutated (≥98% homology) cases, as reported previously. FISH studies were performed using probes for the following regions 13q14, 12q13; 11q22/ATM; 17p13/TP53. Conventional cytogenetic analysis using immunostimulatory CpG-oligonucleotide DSP30 plus IL2 (2μmol/L TibMolBiol / IL2 100U/mL Stem Cell Technologies Inc) was performed on the same samples that had been used for FISH studies. At least 20 metaphases were karyotyped. Stage, time to first treatment (TTFT) were obtained by review of clinical records at each centre.

Results. An abnormal karyotype was found in 30/84 cases (35,7%) with “normal” FISH. The chromosome aberrations affected regions not covered by the 4-probe panel used by FISH. Recurring aberrations were: interstitial deletions of 14q and of 7q in 5 and 3 cases, respectively; 14q32 translocations in 2 cases, balanced and unbalanced structural changes in 1 case each. A complex karyotype with 3 or more aberrations was found in 12 patients. The correlations between karyotype and clinicobiological parameters are shown in tables 1 and 2.

At multivariate analysis, the following factors were independently predictive of shorter TTFT: advanced disease Binet stage (p=0.049, Hazard Ratio 2.39 [se: 1.06]), and abnormal karyotype (p<0.001, Hazard ratio 6.8 [se: 3.28]). IGHV mutations were not included in the TTFT analysis, because the data were not available for all patients.

Conclusions. Conventional karyotyping using odn + IL-2 as mitogens is an effective method for the detection of chromosome aberrations in approximately 1/3 of patients with “normal” FISH on a conventional 4-probe panel. Recurrent aberrations include interstitial deletions at 14q and 7q. The current data show that, in CLL patients with “normal” FISH, conventional cytogenetic analysis using odn + IL-2 identifies a subset of cases with adverse clinical and prognostic features.