M. Stul

Histiocyte-rich B-cell lymphoma. A distinct clinicopathologic entity possibly related to lymphocyte predominant Hodgkin's disease, paragranuloma subtype

This study reports six non-Hodgkins lymphoma cases that we called histiocyte-rich B-cell lymphoma (BCL) because of the prominent reactive histiocytic infiltrate obscuring the malignant B-cell population. The involved lymph nodes are characterized by a mixed nodular and diffuse infiltrate and occasionally feature prominent sinuses. The infiltrate is composed of reactive lymphocytes and numerous histiocytes obscuring a tumor population composed of variably sized scattered cells with irregular or multilobar vesicular nuclei. Immunostaining of paraffin sections for the B-cell marker recognized by L26 helps in the identification of these neoplastic cells. The clonal nature and further evidence of the B-cell lineage of this condition is shown by immunoglobulin gene rearrangements detected in three cases. The six cases of histiocyte-rich BCL are remarkably similar clinically: all presented with stage IVB disease with splenomegaly and follow an aggressive clinical course. Except for these features, our series show striking similarities to paragranuloma lymphocyte-predominant Hodgkins disease, including male preponderance (all patients are male), age distribution (mean age, 41 years), propensity to progress to a diffuse, large B-cell lymphoma (two cases), as well as morphology of the neoplastic B-cell population and expression of Hodgkins cell markers (Leu-M1 positivity after neuraminidase digestion in three cases, Leu-M1 positivity without neuraminidase digestion in one case, and additional epithelial membrane antigen [EMA] positivity in two cases). Both morphologically and clinically, the present series can be differentiated from other types of infiltrate-rich BCL, such as T-cell-rich BCL. Although additional cases will have to be recognized, histiocyte-rich B-cell lymphoma most likely represents a distinct clinicopathological entity. We speculate that it develops from a subset of B cells that also gives rise to the lymphocytic-histocytic (L/H) cell, the Hodgkins cell variant of lymphocyte-predominant Hodgkins disease, paragranuloma subtype.

Characteristic pattern of chromosomal gains and losses in marginal zone B cell lymphoma detected by comparative genomic hybridization

Marginal zone B cell lymphoma (MZBCL) represents a distinct subtype of B cell non-Hodgkin’s lymphoma, which has been recently recognized and defined as a disease entity. We investigated 25 cases (18 at primary diagnosis and seven during the course of disease) of MZBCL by comparative genomic hybridization (CGH) and compared these results with cytogenetic, fluorescence in situ hybridization (FISH), and Southern blot data. Twenty of the 25 cases (80%) showed gains (total 49) or losses (total 15) of genetic material. In extranodal, nodal, and splenic MZBCL, material of chromosomes 3 (52% of cases), 18 (32%), X (24%), and 1q (16%) was most frequently gained, whereas losses predominantly involved chromosomes 17 (16%) and 9 (12%). High-level amplifications involving the regions 18q21-23 and 18q21-22, respectively, were detected in two cases. Gains of chromosomes 1q and 8q and losses of chromosome 17 or 17p occurred more frequently in relapsed or progressive lymphomas. For all of the frequently affected chromosomes, CGH allowed narrowing of the relevant subregions including 3q21-23, 3q25-29 and 18q21-23. By Southern blot analysis, the BCL2, BCL6, and CMYC proto-oncogenes were found to be a part of the over-represented regions in two cases, one case, and two cases, respectively, with gains involving 18q, 3q or 8q. In 13 cases, CGH revealed chromosomal imbalances which were not detected by cytogenetic analysis but could be confirmed by FISH or Southern blot analysis in all cases investigated. On the other hand, CGH failed to detect trisomy 3, trisomy 18, and deletion 7q in three cases with a low proportion of tumor cells bearing these abnormalities, as shown by interphase FISH. The characteristic pattern of chromosomal gains and losses detected in this study confirms the distinct nature of MZBCL and may point to chromosomal regions involved in the pathogenesis of these neoplasms.

Trisomy 3 in marginal zone B-cell lymphoma: A study based on cytogenetic analysis and fluorescence in situ hybridization

Trisomy 3 represents the most frequent and consistent chromosomal abnormality characterizing the recently defined entity marginal zone B‐cell lymphoma (MZBCL). By cytogenetic analysis and/or fluorescence in situ hybridization (FISH) on interphase nuclei we found an increased copy number of chromosome 3 in 22/36 (61%) successfully analysed cases, including 8/12 cases with extranodal MZBCL, 8/13 cases with nodal MZBCL, and 6/11 patients with splenic MZBCL. Sensitivity of interphase cytogenetics was somewhat higher than that of conventional cytogenetic investigation. Structural chromosomal changes involving at least one chromosome 3 were seen in 11/20 cases with an increased copy number of chromosome 3: +del(3)(p13) was demonstrated in three cases, and was the sole chromosomal abnormality in one of them; +i(3)(q10) was seen in two other patients; and rearrangements involving various breakpoints on the long arm of chromosome 3 were found in the remaining cases. FISH on metaphase spreads confirmed these structural abnormalities and additionally showed two unexpected translocations involving chromosome 3. We conclude that: (1) trisomy 3 occurs in a high proportion of extranodal, nodal and splenic MZBCL; (2) FISH on interphase nuclei is an additional and sensitive tool in detecting an increased copy number of chromosome 3 in MZBCL; (3) additional structural abnormalities involving the long arm of chromosome 3 are frequent but non‐recurrent and are perhaps secondary changes; and (4) abnormalities such as +del(3)(p13) and +i(3)(q10) suggest that genes located on the long arm of chromosome 3 are of particular importance in the pathogenesis of MZBCL.

Chromosomal translocations independently predict treatment failure, treatment-free survival and overall survival in B-cell chronic lymphocytic leukemia patients treated with cladribine

Chromosomal translocations represent an important prognostic indicator in B-cell chronic lymphocytic leukemia (B-CLL). However, their value had been neither determined in homogeneously treated patients nor compared to that of IgVH mutational status. Sixty-five B-CLL patients were investigated using cytogenetics, interphase fluorescence in situ hybridization (FISH), analysis of IgVH and of TP53 mutational status before treatment with 2-chloro-2′-deoxyadenosine (CdA). Translocations (n=45) were detected in 42% of the patients, including both balanced (n=12) and unbalanced (n=33) types. IgVH was mutated in 43% of the patients. Patients with translocations were more heavily pretreated (P=0.05), presented with more complex karyotypes (P<0.001), 17p abnormalities and TP53 mutations, and had a higher failure rate (59 vs 21% in patients without translocations, P=0.004). Patients with unbalanced translocations displayed a shorter median treatment-free survival (TFS, 6.9 vs 35.9 months, log rank 22.72, P<0.001) and overall survival (OS, 13.0 vs 68.0 months, log rank 16.51, P<0.001), as compared to patients without translocation. In multivariate analysis, unbalanced translocations were independently associated with therapeutic failure, short TFS and short OS. IgVH mutational status was independently associated with risk of failure and TFS, but not OS. In B-CLL patients treated with CdA, translocations are strong predictors of outcome.

BCL6 gene rearrangements also occur in marginal zone B‐cell lymphoma

Marginal zone B‐cell lymphoma (MZBCL) represents a distinct subtype of B‐cell non‐Hodgkins lymphoma (NHL) which has been recently recognized and defined as a disease entity. Cytogenetically, these lymphomas reveal a high prevalence of trisomy 3, and recent data obtained by comparative genomic hybridization indicate that the chromosomal regions 3q21‐23 and 3q25‐29 might be of particular pathogenetic significance. We identified structural chromosomal abnormalities involving the region 3q27 and rearrangements of the BCL6 proto‐oncogene in three out of 34 (9%) well‐defined cases of extranodal, nodal and splenic MZBCL using cytogenetic analysis, Southern blot, and fluorescence in situ hybridization (FISH). All three cases were characterized by a t(3;14)(q27;q32). Two of them showed additional chromosomal abnormalities including trisomy 3, which was found in one case. The patients displayed extranodal disease and did not demonstrate any striking clinical and histological differences when compared with MZBCL lacking BCL6 rearrangement. The present study for the first time demonstrates the occurrence of t(3;14)/BCL6 gene rearrangement in MZBCL, thus suggesting a role of the BCL6 proto‐oncogene in the pathogenesis of MZBCL.

Translocation t(1;6)(p35.3;p25.2): a new recurrent aberration in ‘unmutated’ B-CLL

Although reciprocal chromosomal translocations are not typical for B-cell chronic lymphocytic leukemia (B-CLL), we identified the novel t(1;6)(p35.3;p25.2) in eight patients with this disorder. Interestingly, all cases showed lack of somatically mutated IgVH. Clinical, morphological, immunologic, and genetic features of these patients are described. Briefly, the age ranged from 33 to 81 years (median: 62.5 years) and the sex ratio was 6M:2F. Most of the patients (6/8) presented with advanced clinical stage. Therapy was required in seven cases. After a median follow-up of 28 months, five patients are alive and three died from disease evolution. Three cases developed transformation into diffuse large B-cell lymphoma. Translocation t(1;6) was found as the primary karyotypic abnormality in three patients. Additional chromosomal aberrations included changes frequently found in unmutated B-CLL, that is, del(11)(q), trisomy 12 and 17p aberrations. Fluorescence in situ hybridization analysis performed in seven cases allowed us to map the t(1;6) breakpoints to the 1p35.3 and 6p25.2 chromosomal bands, respectively. The latter breakpoint was located in the genomic region coding for MUM1/IRF4, one of the key regulators of lymphocyte development and proliferation, suggesting involvement of this gene in the t(1;6). Molecular characterization of the t(1;6)(p35.3;p25.2), exclusively found in unmutated subtype of B-CLL, is in progress.

Primary diffuse large B cell lymphoma of the stomach : analysis of somatic mutations in the rearranged immunoglobulin heavy chain variable genes indicates antigen selection

Gastric low grade MALT lymphomas show a pattern of somatic mutations in their rearranged immunoglobulin genes, indicative of antigen selection. This provides evidence for antigen stimulation in the lymphomagenesis. Gastric diffuse large B cell lymphomas develop secondary to low grade MALT lymphoma or de novo. To study whether antigen-selection is also a feature of primary diffuse large B cell lymphomas, we analysed somatic mutations in the rearranged immunoglobulin heavy chain (IgH) variable genes (VH). The rearranged VH genes of six cases of gastric primary diffuse large B cell lymphoma were amplified from genomic or complementary DNA by a VH gene family-specific polymerase chain reaction method. The PCR products were directly sequenced and were compared to published germline sequences to analyse somatic mutations. Similarly to low grade MALT lymphomas 5/6 primary diffuse large B cell lymphomas show a pattern of somatic mutation in their rearranged VH genes, indicative of antigen selection and suggesting a role for antigens in lymphomagenesis. One case showed bi-allelic VH gene rearrangements, which were non-functional due to extensive deletions. Antigen selection could not be demonstrated or excluded. Antigen selection is a common feature in most analysed primary diffuse large B cell lymphomas, although some heterogeneity in the mechanisms involved in the lymphomagenesis of gastric primary diffuse large B cell lymphomas has not been excluded entirely (case 4).