Structural Alterations of the 14q32/IGH Locus in CLL Revealed by Fluorescence In Situ Hybridization and Array-Based Comparative Genomic Hybridization
RL Sargent, LV Abruzzo, MJ Keating, WG Wierda, LJ Medeiros, R Luthra, D Jones. UT-MD Anderson Cancer Center, Houston, TX
Background: In chronic lymphocytic leukemia (CLL) alterations of the immunoglobulin heavy chain (IGH) locus on chromosome 14q32 have prognostic significance; however, their structure and frequency are poorly characterized. In our study we used fluorescence in situ hybridization (FISH) and array-based comparative genomic hybridization (CGH) to better characterize these alterations.
Design: Within our database we identified 66/2759 CLL cases (2.4%) with 14q32 alterations by conventional karyotypic analysis (CC), of which 85% were of IGH-unmutated type. We performed FISH and CGH in a subset of these cases (9 bone marrow), and compared them to cases without a history of 14q32 alterations by CC (7 bone marrow and 2 peripheral blood) and to 5 normal controls. FISH was performed using a break-apart probe to the IGH locus (Vysis) on either interphase cells or formalin-fixed, paraffin-embedded tissue sections. CGH was performed using a custom-designed CGH array that contained 44,000 60-mer oligonucleotide probes with an average spatial resolution of 75 kilobases augmented with additional probes spanning the IGH gene locus (Agilent Technologies) and labeled genomic DNA hybridized against labeled pooled normal reference DNA.
Results: 5/9 cases (55%) with 14q32 alterations by CC showed IGH rearrangements by FISH, of which 4/5 (80%) appeared non-balanced by CGH, with 0.1-0.3 megabase (mb) deletions in the IGH locus. Of the 4/9 remaining cases with 14q32 alterations by CC, 2 showed deletions of IGH/14q32 by FISH/CGH and 2 showed no detectable alterations by FISH/CGH. 2/9 cases without 14q32 abnormalities by CC showed deletions of IGH/14q32 by FISH/CGH. The remaining 7/9 cases without 14q32 abnormalities by CC did not demonstrate abnormalities by FISH but showed 0.1-0.5 mb deletions within the IGH loci by CGH. No significant 14q32/IGH alterations were noted by CGH in 4 normal samples.
Conclusions: Although CC identifies alterations of 14q32 in a small percentage of CLL cases (largely restricted to the unmutated subtype), FISH and CGH identify additional 14q32 alterations, including apparent cryptic translocations and deletions of the IGH locus. Further, a customized array design provides additional accuracy in delineating the IGH/14q32 aberrations compared to FISH. The high incidence of small deletions within the IGH locus identified by CGH may reflect normal lineage-associated VDJ recombination, or tumor-associated genetic instability or promiscuous recombination.
Tuesday, March 10, 2009 9:30 AM
Poster Session III # 114, Tuesday Morning