BCL6 gene rearrangement and protein expression are associated with large cell presentation of extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue

Molecular characterization of diffuse large B-cell lymphomas associated with hepatitis C virus infection

Hepatitis C virus (HCV)-associated diffuse large B-cell lymphoma (DLBCL) displays peculiar clinicopathological characteristics, but its molecular landscape is not fully elucidated. In this study, we investigated the clinicopathological and molecular features of 54 patients with HCV-associated DLBCL. The median age was 71 years. An underlying marginal zone lymphoma component was detected in 14.8% of cases. FISH analysis showed rearrangements involving BCL6 in 50.9% of cases, MYC in 11.3% and BCL2 in 3.7%. Lymph2Cx-based assay was successful in 38 cases, recognizing 16 cases (42.1%) as ABC and 16 cases as GCB subtypes, while six resulted unclassified. ABC cases exhibited a higher lymphoma-related mortality (LRM). Next-generation sequencing analysis showed mutations in 158/184 evaluated genes. The most frequently mutated genes were KMT2D (42.6%), SETD1B (33.3%), RERE (29.4%), FAS and PIM1 (27.8%) and TBL1XR1 (25.9%). A mutation in the NOTCH pathway was detected in 25.9% of cases and was associated with worst LRM. Cluster analysis by LymphGen classified 29/54 cases within definite groups, including BN2 in 14 (48.2%), ST2 in seven (24.2%) and MCD and EZB in four each (13.8%). Overall, these results indicate a preferential marginal zone origin for a consistent subgroup of HCV-associated DLBCL cases and suggest potential implications for molecularly targeted therapies.

The genetic landscape of histologically transformed marginal zone lymphomas

BACKGROUND

Marginal zone lymphomas (MZLs) comprise a diverse group of indolent lymphoproliferative disorders; however, some patients develop histologic transformation (HT) with rapid progression to aggressive lymphoma.

METHODS

Forty-three MZLs with HT (HT-MZLs), 535 MZLs, and 174 de novo diffuse large B-cell lymphomas (DLBCLs) without rearrangements of MYC, BCL2, and BCL6 were collected. Among these, 22 HT-MZLs, 39 MZLs, and 174 DLBCLs were subjected to 148-gene targeted exome sequencing. The clinicopathologic features of patients who had HT-MZL and their genetic alterations were compared with those of patients who had MZLs and DLBCLs.

RESULTS

All 43 HT-MZLs corresponded to DLBCLs. No HT-MZLs harbored BCL2 and MYC and/or BCL6 rearrangements. Bone marrow involvement and higher levels of lactate dehydrogenase were significantly more common in HT-MZLs than in MZLs. Furthermore, upregulated BCL6, MUM1, C-MYC, and Ki-67 expression was observed more frequently in HT-MZLs than in MZLs. TBL1XR1 was the most frequently altered gene (63.6%) in HT-MZLs, followed by CCND3 (31.8%), CARD11, ID3, and TP53 (22.7%). A trend toward worse progression-free survival in patients with TBL1XR1 mutations was observed. Compared with MZLs and non-germinal center B-cell (GCB) type DLBCLs, significantly higher frequencies of TBL1XR1 and ID3 mutations were identified in HT-MZLs. PIM1 mutations frequently occurred in DLBCLs and were significantly associated with TBL1XR1 mutations but were mutated less in HT-MZLs that had TBL1XR1 mutations.

CONCLUSIONS

The current findings reveal the clinicopathologic and genetic features of HT-MZLs, suggesting that these tumors might constitute a group distinct from MZL and de novo non-GCB type DLBCL. TBL1XR1 mutations may be considered a predictor of HT in MZL.

Frequent mutations of FBXO11 highlight BCL6 as a therapeutic target in Burkitt lymphoma

The expression of BCL6 in B cell lymphoma can be deregulated by chromosomal translocations, somatic mutations in the promoter regulatory regions or reduced proteasome-mediated degradation. FBXO11 was recently identified as a ubiquitin ligase involved in the degradation of BCL6 and is frequently inactivated in lymphoma or other tumors. Here, we show that FBXO11 mutations are found in 23% of Burkitt lymphoma (BL) patients. FBXO11 mutations impaired BCL6 degradation and the deletion of FBXO11 protein completely stabilized BCL6 levels in human BL cell lines. Conditional deletion of either one or two copies of the FBXO11 gene in mice cooperated with oncogenic MYC and accelerated B cell lymphoma onset, providing experimental evidence that FBXO11 is a haplo-insufficient oncosuppressor in B cell lymphoma. In WT and FBXO11-deficient BL mouse and human cell lines, targeting BCL6 via specific degrader or inhibitors partially impaired lymphoma growth in vitro and in vivo. Inhibition of MYC by the Omomyc mini-protein blocked cell proliferation and increased apoptosis, effects further increased by combined BCL6 targeting. Thus, by validating the functional role of FBXO11 mutations in BL we further highlight the key role of BCL6 in BL biology and provide evidence that innovative therapeutic approaches such as BCL6 degraders and direct MYC inhibition could be exploited as a targeted therapy for BL.

Genome-wide DNA methylation analysis along the progression of gastric marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) type

Extra-nodal marginal zone B-cell lymphoma (MZBL) of mucosa-associated lymphoid tissue is an indolent lymphoma mostly affecting the gastrointestinal tract. The lymphoma initially has small-cell morphology (SC-MZBL) and often arises in the background of Helicobacter pylori-induced gastritis. In some cases, a clonal malignant progression to large-cell morphology (LC-MZBL) is observed. Here, we studied the DNA methylation profile of 30 gastric MZBLs along their progression. Genome-wide DNA methylation profiling, identified 7698 significantly differentially methylated loci during gastric MZBL progression (σ/σ_max ≥0·4, q ≤ 0·001). LC-MZBL showed hypermethylation in comparison to SC-MZBL with an enrichment of regions involved in transcriptional regulation. In conclusion, our present data show that the morphological distinction between SC- and LC-MZBL is reflected by characteristic DNA methylation profiles.

Recent advances upper gastrointestinal lymphomas: molecular updates and diagnostic implications

Approximately one-third of extranodal non-Hodgkin lymphomas involve the gastrointestinal (GI) tract, with the vast majority being diagnosed in the stomach, duodenum, or proximal small intestine. A few entities, especially diffuse large B-cell lymphoma and extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue, represent the majority of cases. In addition, there are diseases specific to or characteristic of the GI tract, and any type of systemic lymphoma can present in or disseminate to these organs. The recent advances in the genetic and molecular characterisation of lymphoid neoplasms have translated into notable changes in the classification of primary GI T-cell neoplasms and the recommended diagnostic approach to aggressive B-cell tumours. In many instances, diagnoses rely on morphology and immunophenotype, but there is an increasing need to incorporate molecular genetic markers. Moreover, it is also important to take into consideration the endoscopic and clinical presentations. This review gives an update on the most recent developments in the pathology and molecular pathology of upper GI lymphoproliferative diseases.

Expression of germinal center cell markers by extranodal marginal zone lymphomas of MALT type within colonized follicles, a diagnostic pitfall with follicular lymphoma

We reviewed 341 consecutive cases of marginal zone lymphoma (MZL) (47) or follicular lymphoma (FL) (294) of which 7 were difficult to distinguish due to perceived coexpression of BCL6 and BCL2 by tumor cells in follicular foci. This stimulated us to develop dual BCL6/BCL2 immunohistochemistry, allowing us to assess coexpression among individual cells. Dual staining confirmed coexpression in 6 of 7 cases, all extranodal MZL (ENMZL) based on overall features and representing 13% of MZL in this series. These findings confirm that MZL cells have plasticity regarding protein expression within the germinal center (GC) microenvironment, an important diagnostic pitfall. Intriguingly, in all MZL expressing BCL6, non-neoplastic GC B cells within colonized follicles showed diminished or absent CD10 expression but preserved BCL6 and high ki67. This finding suggests plasticity of CD10 expression in non-neoplastic GC B cells in the context of colonization by MZL, possibly related to NF-kB dysregulation.

Impact of Genetics on Mature Lymphoid Leukemias and Lymphomas

Recurrent genetic aberrations have long been recognized in mature lymphoid leukemias and lymphomas. As conventional karyotypic and molecular cloning techniques evolved in the 1970s and 1980s, multiple cytogenetic aberrations were identified in lymphomas, often balanced translocations that juxtaposed oncogenes to the immunoglobulin (IG) or T-cell receptor (TR) loci, leading to dysregulation. However, genetic characterization and classification of lymphoma by conventional cytogenetic methods is limited by the infrequent occurrence of recurrent karyotypic abnormalities in many lymphoma subtypes and by the frequent difficulty in growing clinical lymphoma specimens in culture to obtain informative karyotypes. As higher-resolution genomic techniques developed, such as array comparative genomic hybridization and fluorescence in situ hybridization, many recurrent copy number changes were identified in lymphomas, and copy number assessment of interphase cells became part of routine clinical practice for a subset of diseases. Platforms to globally examine mRNA expression led to major insights into the biology of several lymphomas, although these techniques have not gained widespread application in routine clinical settings. With the advent of next-generation sequencing (NGS) techniques in the early 2000s, numerous insights into the genetic landscape of lymphomas were obtained. In contrast to the myeloid malignancies, most common lymphomas exhibit an at least somewhat mutationally complex genome, with few single driver mutations in the majority of patients. However, many recurrently mutated pathways have been identified across lymphoma subtypes, informing targeted therapeutic approaches that are beginning to make meaningful changes in the treatment of lymphoma. In addition to the ability to identify possible therapeutic targets, NGS techniques are highly amenable to the tracking of residual lymphoma following therapy, because of the presence of unique genetic "fingerprints" in lymphoma cells due to V(D)-J recombination at the antigen receptor loci. This review will provide an overview of the impact of novel genetic technologies on lymphoma classification, biology, and therapy.

A Probabilistic Classification Tool for Genetic Subtypes of Diffuse Large B Cell Lymphoma with Therapeutic Implications

The development of precision medicine approaches for diffuse large B cell lymphoma (DLBCL) is confounded by its pronounced genetic, phenotypic, and clinical heterogeneity. Recent multiplatform genomic studies revealed the existence of genetic subtypes of DLBCL using clustering methodologies. Here, we describe an algorithm that determines the probability that a patient's lymphoma belongs to one of seven genetic subtypes based on its genetic features. This classification reveals genetic similarities between these DLBCL subtypes and various indolent and extranodal lymphoma types, suggesting a shared pathogenesis. These genetic subtypes also have distinct gene expression profiles, immune microenvironments, and outcomes following immunochemotherapy. Functional analysis of genetic subtype models highlights distinct vulnerabilities to targeted therapy, supporting the use of this classification in precision medicine trials.

Epigenetic Programing of B-Cell Lymphoma by BCL6 and Its Genetic Deregulation

B cell lymphoma is a clinically heterogeneous and pathologically diverse group of diseases with a strong epigenetic component. The B cell lymphoma 6 (BCL6) gene encodes a transcription factor that is critical for normal germinal center reaction B cell development by maintaining an epigenetic and transcriptional state that is permissive for cellular proliferation and DNA damage. The activity of BCL6 can be deregulated by a variety of mechanisms and contributes to the development of B-cell lymphoma. Here we review the direct and indirect mechanisms BCL6 dysregulation in B cell lymphoma, including transcriptional and post-translational regulation of BCL6 expression and activity, and the perturbation of BCL6-regulated epigenetic programs by cooperating chromatin modifying gene mutations. We underscore the critical importance of BCL6 and its associated epigenetic programs in the development of B-cell lymphoma, and discuss avenues for the therapeutic targeting of BCL6 in this context.

Taming the Heterogeneity of Aggressive Lymphomas for Precision Therapy

Genomic analyses of diffuse large B cell lymphoma (DLBCL) are revealing the genetic and phenotypic heterogeneity of these aggressive lymphomas. In part, this heterogeneity reflects the existence of distinct genetic subtypes that acquire characteristic constellations of somatic genetic alterations to converge on the DLBCL phenotype. In parallel, functional genomic screens and proteomic analyses have identified multiprotein assemblies that coordinate oncogenic survival signaling in DLBCL. In this review, we merge these recent insights into a unified conceptual framework with implications for the design of precision medicine trials in DLBCL.

Molecular subtypes of diffuse large B cell lymphoma are associated with distinct pathogenic mechanisms and outcomes

Diffuse large B cell lymphoma (DLBCL), the most common lymphoid malignancy in adults, is a clinically and genetically heterogeneous disease that is further classified into transcriptionally defined activated B cell (ABC) and germinal center B cell (GCB) subtypes. We carried out a comprehensive genetic analysis of 304 primary DLBCLs and identified low-frequency alterations, captured recurrent mutations, somatic copy number alterations, and structural variants, and defined coordinate signatures in patients with available outcome data. We integrated these genetic drivers using consensus clustering and identified five robust DLBCL subsets, including a previously unrecognized group of low-risk ABC-DLBCLs of extrafollicular/marginal zone origin; two distinct subsets of GCB-DLBCLs with different outcomes and targetable alterations; and an ABC/GCB-independent group with biallelic inactivation of TP53, CDKN2A loss, and associated genomic instability. The genetic features of the newly characterized subsets, their mutational signatures, and the temporal ordering of identified alterations provide new insights into DLBCL pathogenesis. The coordinate genetic signatures also predict outcome independent of the clinical International Prognostic Index and suggest new combination treatment strategies. More broadly, our results provide a roadmap for an actionable DLBCL classification.

Genetics and Pathogenesis of Diffuse Large B-Cell Lymphoma

BACKGROUND

Diffuse large B-cell lymphomas (DLBCLs) are phenotypically and genetically heterogeneous. Gene-expression profiling has identified subgroups of DLBCL (activated B-cell-like [ABC], germinal-center B-cell-like [GCB], and unclassified) according to cell of origin that are associated with a differential response to chemotherapy and targeted agents. We sought to extend these findings by identifying genetic subtypes of DLBCL based on shared genomic abnormalities and to uncover therapeutic vulnerabilities based on tumor genetics.

METHODS

We studied 574 DLBCL biopsy samples using exome and transcriptome sequencing, array-based DNA copy-number analysis, and targeted amplicon resequencing of 372 genes to identify genes with recurrent aberrations. We developed and implemented an algorithm to discover genetic subtypes based on the co-occurrence of genetic alterations.

RESULTS

We identified four prominent genetic subtypes in DLBCL, termed MCD (based on the co-occurrence of MYD88L265P and CD79B mutations), BN2 (based on BCL6 fusions and NOTCH2 mutations), N1 (based on NOTCH1 mutations), and EZB (based on EZH2 mutations and BCL2 translocations). Genetic aberrations in multiple genes distinguished each genetic subtype from other DLBCLs. These subtypes differed phenotypically, as judged by differences in gene-expression signatures and responses to immunochemotherapy, with favorable survival in the BN2 and EZB subtypes and inferior outcomes in the MCD and N1 subtypes. Analysis of genetic pathways suggested that MCD and BN2 DLBCLs rely on "chronic active" B-cell receptor signaling that is amenable to therapeutic inhibition.

CONCLUSIONS

We uncovered genetic subtypes of DLBCL with distinct genotypic, epigenetic, and clinical characteristics, providing a potential nosology for precision-medicine strategies in DLBCL. (Funded by the Intramural Research Program of the National Institutes of Health and others.).

Novel developments in the pathogenesis and diagnosis of extranodal marginal zone lymphoma

Extranodal marginal zone lymphoma (EMZL), mostly represented by mucosa-associated lymphoid tissue (MALT) type, also referred to as MALT lymphoma, is a clinically heterogeneous entity within the group of low-grade B cell lymphomas that arises in a wide range of different extranodal sites, including the stomach, lung, ocular adnexa, and skin. It represents the third most common non-Hodgkin lymphoma in the Western world, and the median age of occurrence is around 60 years. One characteristic aspect in a subset of EMZL detectable in about 25% of the cases is the presence of specific chromosomal translocations involving the genes MALT1 and BCL10, which lead to activation of the NF-κB signaling pathway. Another unique aspect is that several infectious agents, such as Helicobacter pylori in the case of gastric EMZL, and autoimmune disorders, like Sjögren syndrome, have been implicated in the pathogenesis of this cancer. Recent findings as summarized in this review have further improved our understanding of the complex pathobiology of this disease and have been essential to better define novel treatment strategies. In addition, many of these specific features are currently being implemented for the diagnosis of EMZL.

Comparative gene-expression profiling of the large cell variant of gastrointestinal marginal-zone B-cell lymphoma

Gastrointestinal (g.i.) large cell lymphoma is currently regarded as diffuse large B-cell lymphoma (DLBCL) despite a more favorable clinical outcome compared to other DLBCL. Cluster analyses on a transcriptome signature of NF-κB target genes of 30 g.i. marginal zone B-cell lymphomas (MZBL; 8 g.i. MZBL, 22 large cell MZBL - among them 9 with coexisting small cell component) and 6 DLBCL (3 activated B-cell like (ABC), 3 germinal center-like (GCB)) reveals a distinct pattern. The distinctiveness of large cell MZBL samples is further confirmed by a cohort of 270 available B-cell lymphoma and B-cell in silico profiles. Of the NF-κB genes analyzed, c-REL was overexpressed in g.i. MZBL. c-REL amplification was limited to 6/22 large cell MZBL including the large cell component of 2/9 composite small cell/large cell lymphomas, and c-Rel protein expression was found in the large cell compartment of composite lymphomas. Classification experiments on DLBCL and large cell MZBL profiles support the concept that the large cell MZBL is a distinct type of B-cell lymphoma.

High-grade Transformation of Low-grade B-cell Lymphoma: Pathology and Molecular Pathogenesis

Patients with low-grade (clinically indolent) lymphomas are at risk to undergo transformation to high-grade (clinically aggressive) lymphoma, although transformation only occurs in a subset of patients. When transformation occurs it is a critical event that determines the course of disease and is associated with unfavorable patient outcomes. Accurate detection of transformation, predictive biomarkers, and identification of specific molecular pathways implicated in the pathobiology of transformation will facilitate personalized therapeutic approaches and underpin advances in clinical outcomes. In this article, we present an update of the clinical and pathologic diagnostic criteria for low-grade B-cell lymphoma transformation and discuss the molecular alterations involved in the pathogenesis of this biological phenomenon.

Role of Helicobacter pylori in gastric mucosa-associated lymphoid tissue lymphomas

Mucosa-associated lymphoid tissue (MALT) lymphoma is an indolent extranodal marginal zone B-cell lymphoma, originating in acquired MALT that is induced in mucosal barriers as part of a normal adaptive immune response to a chronic immunoinflammatory stimulus, most notably chronic infection by Helicobacter pylori (H. pylori). This antigenic stimulation initially leads to lymphoid hyperplasia; the acquisition of additional genetic aberrations culminates in the activation of intracellular survival pathways, with disease progression due to proliferation and resistance to apoptosis, and the emergence of a malignant clone. There are descriptions of MALT lymphomas affecting practically every organ and system, with a marked geographic variability partially attributable to the epidemiology of the underlying risk factors; nevertheless, the digestive system (and predominantly the stomach) is the most frequently involved location, reflecting the gastrointestinal tract’s unique characteristics of contact with foreign antigens, high mucosal permeability, large extension and intrinsic lymphoid system. While early-stage gastric MALT lymphoma can frequently regress after the therapeutic reversal of the chronic immune stimulus through antibiotic eradication of H. pylori infection, the presence of immortalizing genetic abnormalities, of advanced disease or of eradication-refractoriness requires a more aggressive approach which is, presently, not consensual. The fact that MALT lymphomas are rare neoplasms, with a worldwide incidence of 1-1.5 cases per 10⁵ population, per year, limits the ease of accrual of representative series of patients for robust clinical trials that could sustain informed evidence-based therapeutic decisions to optimize the quality of patient care.

[Gastric lymphoma: still an interdisciplinary challenge]

Differentiation of chronic gastritis from marginal zone B-cell lymphoma (MZoL) of MALT type is often difficult for the pathologist. Diagnostic tools include CD20 stain to highlight lymphoepithelial lesions, Wotherspoon grading of the infiltrate, and clonality analysis of the B-cells. MZoL may partially transform into a diffuse, large B-cell lymphoma, which the authors have named blastic MZoL. Blastic MZoL may be present with or without small cell MZoL. Without this component, blastic MzoL, while being CD10-negative, is presently difficult to positively diagnose since specific immune markers are still lacking. Blastic MZoL has a very favourable outcome compared to conventional diffuse large B-cell lymphomas (DLBCL). Moreover, there are conventional DLBCL in the stomach, mostly in a setting of a secondary organ involvement. The biology of these gastric DLBCL is identical to their extragastric counterparts. This is also true for primary gastric Burkitt lymphoma and mucosal involvement in B-CLL or mantle cell lymphoma. Unfavourable outcomes are always observed for EBV-triggered lymphoproliferations in immunodeficiency and peripheral T-cell lymphomas which might also arise or be initially diagnosed in the stomach.

Sensitive and specific immunohistochemical diagnosis of human alveolar echinococcosis with the monoclonal antibody Em2G11

Background

Alveolar echinococcosis (AE) is caused by the metacestode stage of Echinococcus multilocularis. Differential diagnosis with cystic echinococcosis (CE) caused by E. granulosus and AE is challenging. We aimed at improving diagnosis of AE on paraffin sections of infected human tissue by immunohistochemical testing of a specific antibody.

Methodology/Principal Findings

We have analysed 96 paraffin archived specimens, including 6 cutting needle biopsies and 3 fine needle aspirates, from patients with suspected AE or CE with the monoclonal antibody (mAb) Em2G11 specific for the Em2 antigen of E. multilocularis metacestodes. In human tissue, staining with mAb Em2G11 is highly specific for E. multilocularis metacestodes while no staining is detected in CE lesions. In addition, the antibody detects small particles of E. multilocularis (spems) of less than 1 µm outside the main lesion in necrotic tissue, liver sinusoids and lymphatic tissue most probably caused by shedding of parasitic material. The conventional histological diagnosis based on haematoxylin and eosin and PAS stainings were in accordance with the immunohistological diagnosis using mAb Em2G11 in 90 of 96 samples. In 6 samples conventional subtype diagnosis of echinococcosis had to be adjusted when revised by immunohistology with mAb Em2G11.

Conclusions/Significance

Immunohistochemistry with the mAb Em2G11 is a new, highly specific and sensitive diagnostic tool for AE. The staining of small particles of E. multilocularis (spems) outside the main lesion including immunocompetent tissue, such as lymph nodes, suggests a systemic effect on the host.

Echinococcosis is a life-threatening disease in humans that is caused by the larval stages of the tapeworms Echinococcus multilocularis and Echinococcus granulosus. The eggs of the parasites are released with faeces of canids, and humans are aberrantly infected. In humans, the larval stages of the parasites cause tumour-like lesions mainly in the liver and the lungs. Precise diagnosis of the parasite responsible for human disease is of utmost importance since therapy regimens largely differ between cystic and alveolar echinococcosis. Diagnosis is based on serology, imaging and histology, the latter being the gold standard. However, conventional histology cannot always clearly identify the causative parasite because both parasites can cause human tissue to present similar features. Therefore, we have developed the monoclonal antibody Em2G11 and an immunohistological technique that allows a cheap and fast clear-cut diagnosis of E. multilocularis even on aspirates and small archived bioptic tissue samples. Furthermore, this technique disclosed an unknown feature of human alveolar echinococosis we called "small particles of E. multilocularis" (spems). We argue that these small particles represent micro-fragments of E. multilocularis and thus point to a new form of host-parasite interaction.

High-resolution genomic profiling reveals clonal evolution and competition in gastrointestinal marginal zone B-cell lymphoma and its large cell variant

We studied marginal zone B-cell lymphomas of the gastrointestinal tract including seven small cell lymphomas, eight large cell areas of composite lymphomas and 13 large cell variants using SNP array profiling. We found an increase of genomic complexity with lymphoma progression from small to large cytology, and identified gains of prominent (proto) oncogenes such as REL, BCL11A, ETS1, PTPN1, PTEN and KRAS which were found exclusively in the large cell variants. Copy numbers of ADAM3A, SCAPER and SIRPB1 were varying between the three different modes of presentation, hence suggestive for aberrations associated with progression from small to large cell lymphoma. The number of aberrations was slightly higher in the large cell part of composite lymphomas than in large cell lymphomas, suggesting that clonal selection takes place and that composite lymphomas are in a transition state. To further investigate this, we comparatively analyzed samples of two morphologically different regions of the same small cell tumor with a BIRC3-MALT1 translocation, as well as material acquired at two different time points from one composite lymphoma. We found genomic heterogeneity in both cases, supporting the theory of competing subclones in the evolution and progression of extranodal marginal zone B-cell lymphoma.