Low-grade B-Cell lymphomas with plasmacytic differentiation lack PAX5 gene rearrangements

Abstract

The chromosomal translocation t(9;14)(p13;q32) has been reported in association with lymphoplasmacytic lymphoma (LPL). Although this translocation involving the paired homeobox-5 (PAX5) gene at chromosome band 9p13 and the immunoglobulin heavy chain (IgH) gene at 14q32 has been described in approximately 50% of LPL cases, the actual number of cases studied is quite small. Many of the initial cases associated with t(9;14)(p13;q32) were actually low-grade B-cell lymphomas with plasmacytic differentiation other than LPL. Thus, we analyzed a series of low-grade B-cell lymphomas for PAX5 gene rearrangements. We searched records from the Department of Pathology, Stanford University Medical Center for low-grade B-cell lymphomas, with an emphasis on plasmacytic differentiation, that had available paraffin blocks or frozen tissue. We identified 37 cases, including 13 LPL, 18 marginal zone lymphomas (nodal, extranodal, splenic, and alpha-heavy chain disease), and 6 small lymphocytic lymphomas. A novel dual-color break-apart bacterial artificial chromosome probe was designed to flank the PAX5 gene, spanning previously described PAX5 breakpoints, and samples were analyzed by interphase fluorescence in situ hybridization. All cases failed to demonstrate a PAX5 translocation, indicating that t(9;14)(p13;q32) and other PAX5 translocations are uncommon events in low-grade B-cell lymphomas with plasmacytic differentiation. This study also confirms recent reports that found an absence of PAX5 rearrangements in LPL, suggesting the reassessment of PAX5 rearrangements in LPL.

Figure 1

PAX-5 FISH probe design. BACs RP11-12P15 and RP11-243F8 (labeled green) span the PAX5 gene and ∼250-kb telomeric (3′) to the PAX5 gene. RP11-501A2 (labeled red) localizes to a region centromeric (5′) to previously described breakpoints. Arrows indicate sequenced PAX-5 translocations described in the literature.,,,,,,, Base position identified using the UCSC Genome Browser, http://genome.ucsc.edu.

Figure 2

Co-hybridization of KIS-1 metaphase spread with the dual-color CBFB probe specific for band 16q22 and differentially labeled whole chromosome paint probes for chromosomes 9 and 14 show two chromosomes consisting primarily of chromosome 9 material (labeled red) and representing a normal 9 homolog and a derivative 9 consistent with a translocation t(9;14). Two additional rearranged chromosomes are identified, a derivative chromosome 14 (labeled green) with a small distal chromosome 9 segment (labeled red), and a complex derivative chromosome 16 [der(16)] identified by the CBFB probe and containing distal juxtaposed red chromosome 9 and green chromosome 14 segments.

Figure 3

KIS-1 metaphase (A) and interphase nuclei (B) hybridized with PAX5 probe. Red signals correspond to the centromeric (5′) end of the PAX5 probe on chromosome 9p13, whereas green signals indicate the telomeric (3′) portion of the probe. A fusion signal indicates an intact PAX5 gene. Separate red and green signals (split signal) indicate a PAX5 rearrangement.

Figure 4

Representative interphase nuclei from case 27 hybridized with PAX5 probe. Two fusion signals indicate intact PAX5 genes with no translocation.

Figure 5

Representative interphase nuclei from case 22 hybridized with PAX5 probe. Four fusion signals indicate duplication of chromosome 9, confirmed by FISH with telomeric 9p and 9q probes (data not shown).