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Primary bone diffuse large B-cell lymphoma (PB-DLBCL) is a rare extranodal lymphoma subtype. This retrospective study elucidates the currently unknown genetic background of a large clinically well-annotated cohort of DLBCL with osseous localizations (O-DLBCL), including PB-DLBCL. A total of 103 patients with O-DLBCL were included and compared with 63 (extra)nodal non-osseous (NO)-DLBCLs with germinal center B-cell phenotype (NO-DLBCL-GCB). Cell-of-origin was determined by immunohistochemistry and gene-expression profiling (GEP) using (extended)-NanoString/Lymph2Cx analysis. Mutational profiles were identified with targeted next-generation deep sequencing, including 52 B-cell lymphoma-relevant genes. O-DLBCLs, including 34 PB-DLBCLs, were predominantly classified as GCB phenotype based on immunohistochemistry (74%) and NanoString analysis (88%). Unsupervised hierarchical clustering of an extended-NanoString/Lymph2Cx revealed significantly different GEP clusters for PB-DLBCL as opposed to NO-DLBCL-GCB (P< .001). Expression levels of 23 genes of 2 different targeted GEP panels indicated a centrocyte-like phenotype for PB-DLBCL, whereas NO-DLBCL-GCB exhibited a centroblast-like constitution. PB-DLBCL had significantly more frequent mutations in four GCB-associated genes (ie, B2M, EZH2, IRF8, TNFRSF14) compared with NO-DLBCL-GCB (P= .031, P= .010, P= .047, and P= .003, respectively). PB-DLBCL, with its corresponding specific mutational profile, was significantly associated with a superior survival compared with equivalent Ann Arbor limited-stage I/II NO-DLBCL-GCB (P= .016). This study is the first to show that PB-DLBCL is characterized by a GCB phenotype, with a centrocyte-like GEP pattern and a GCB-associated mutational profile (both involved in immune surveillance) and a favorable prognosis. These novel biology-associated features provide evidence that PB-DLBCL represents a distinct extranodal DLBCL entity, and its specific mutational landscape offers potential for targeted therapies (eg, EZH2 inhibitors).

Non‐random chromosomal translocations are specifically involved in the pathogenesis of many non‐Hodgkin's lymphomas and have clinical implications as diagnostic and/or prognostic markers. Their detection is often impaired by technical problems, including the distribution of the breakpoints over large genomic areas. This study reports a fluorescence in situhybridization (FISH) method which allows the detection of specific chromosomal breakpoints in tissue sections from routinely fixed, paraffin‐embedded samples. Hybridization was performed after demasking the DNA. Previously validated locus‐specific probes (cosmids, PACs) flanking the BCL1, BCL2regions and similar new probes for the MYCbreakpoint region were used. The cases studied were five mantle cell lymphomas (MCL) and five follicular lymphomas (FL), selected on the basis of a previously proved t(11;14) and t(14;18) and five randomly chosen Burkitt's lymphomas (BL), as well as 21 negative control samples. In all samples, hybridization signals of sufficient intensity were obtained. Three different algorithms were used to score the hybridization signals in tissue sections, two of them taking into account the nuclei and their signal distribution indicative of chromosomal break, and one only considering the colocalization or segregation of the signals. In control tissues, these algorithms resulted in cut‐off levels of 9.1%, 1.3%, or 10.0%. In the 15 lymphoma samples the percentages of abnormal cells/signals ranged from 28% to 80%, 13% to 49%, and 40% to 70%, respectively. The results indicate that small locus‐specific probes can be used in FISH for regular detection of translocation breakpoints on routine paraffin tissue sections. Copyright © 2002 John Wiley & Sons, Ltd.

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