Splenic marginal zone lymphoma: characterization of 7q deletion and its value in diagnosis

The genomic and molecular landscape of splenic marginal zone lymphoma, biological and clinical implications

Splenic marginal zone lymphoma (SMZL) is a rare, predominantly indolent B-cell lymphoma constituting fewer than 2% of lymphoid neoplasms. However, around 30% of patients have a shorter survival despite currently available treatments and the prognosis is especially poor for the 5-15% of cases that transform to a large cell lymphoma. Mounting evidence suggests that the molecular pathogenesis of SMZL is critically shaped by microenvironmental triggering and cell-intrinsic aberrations. Immunogenetic investigations have revealed biases in the immunoglobulin gene repertoire, indicating a role of antigen selection. Furthermore, cytogenetic studies have identified recurrent chromosomal abnormalities such as deletion of the long arm of chromosome 7, though specific disease-associated genes remain elusive. Our knowledge of SMZL's mutational landscape, based on a limited number of cases, has identified recurring mutations in KLF2, NOTCH2, and TP53, as well as genes clustering within vital B-cell differentiation pathways. These mutations can be clustered within patient subgroups with different patterns of chromosomal lesions, immunogenetic features, transcriptional signatures, immune microenvironments, and clinical outcomes. Regarding SMZL epigenetics, initial DNA methylation profiling has unveiled epigenetically distinct patient subgroups, including one characterized by elevated expression of Polycomb repressor complex 2 (PRC2) components. Furthermore, it has also demonstrated that patients with evidence of high historical cell division, inferred from methylation data, exhibit inferior treatment-free survival. This review provides an overview of our current understanding of SMZL's molecular basis and its implications for patient outcomes. Additionally, it addresses existing knowledge gaps, proposes future research directions, and discusses how a comprehensive molecular understanding of the disease will lead to improved management and treatment choices for patients.

The many faces of nodal and splenic marginal zone lymphomas. A report of the 2022 EA4HP/SH lymphoma workshop

Session 3 of the lymphoma workshop of the XXI joint meeting of the European Association for Haematopathology and the Society for Hematopathology took place in Florence, Italy, on September 22, 2022. The topics of this session were splenic and nodal marginal zone lymphomas, transformation in marginal zone lymphomas, and pediatric nodal marginal zone lymphomas and their differential diagnosis as well as related entities. Forty-two cases in these categories were submitted to the workshop, including splenic lymphomas (marginal zone and diffuse red pulp lymphomas), transformed marginal zone lymphomas (splenic and nodal), nodal marginal zone lymphomas with increased TFH-cells, and pediatric nodal marginal zone lymphomas. The case review highlighted some of the principal problems in the diagnosis of marginal zone lymphomas, including the difficulties in the distinction between splenic marginal zone lymphoma, splenic diffuse red pulp lymphoma, and hairy cell leukemia variant/splenic B-cell lymphoma with prominent nucleoli which requires integration of clinical features, immunophenotype, and morphology in blood, bone marrow, and spleen; cases of marginal zone lymphoma with markedly increased TFH-cells, simulating a T-cell lymphoma, where molecular studies (clonality and mutation detection) can help to establish the final diagnosis; the criteria for transformation of marginal zone lymphomas, which are still unclear and might require the integration of morphological and molecular data; the concept of an overlapping spectrum between pediatric nodal marginal zone lymphoma and pediatric-type follicular lymphoma; and the distinction between pediatric nodal marginal zone lymphoma and "atypical" marginal zone hyperplasia, where molecular studies are mandatory to correctly classify cases.

Krüppel-like factor 2: a central regulator of B cell differentiation and plasma cell homing

The development of B cells, their activation and terminal differentiation into antibody-producing plasma cells are characterized by alternating phases of proliferation and quiescence that are controlled by complex transcriptional networks. The spatial and anatomical organization of B cells and plasma cells inside lymphoid organs as well as their migration within lymphoid structures and between organs are prerequisites for the generation and the maintenance of humoral immune responses. Transcription factors of the Krüppel-like family are critical regulators of immune cell differentiation, activation, and migration. Here, we discuss the functional relevance of Krüppel-like factor 2 (KLF2) for B cell development, B cell activation, plasma cell formation and maintenance. We elaborate on KLF2-mediated regulation of B cell and plasmablast migration in the context of immune responses. Moreover, we describe the importance of KLF2 for the onset and the progression of B cell-related diseases and malignancies.

New Insights into the Biology and Diagnosis of Splenic Marginal Zone Lymphomas

Splenic marginal zone lymphoma (SMZL) is a small B-cell lymphoma, which has been recognized as a distinct pathological entity since the WHO 2008 classification. It classically presents an indolent evolution, but a third of patients progress rapidly and require aggressive treatments, such as immuno-chemotherapy or splenectomy, with all associated side effects. In recent years, advances in the comprehension of SMZL physiopathology have multiplied, thanks to the arrival of new devices in the panel of available molecular biology techniques, allowing the discovery of new molecular findings. In the era of targeted therapies, an update of current knowledge is needed to guide future researches, such as those on epigenetic modifications or the microenvironment of these lymphomas.

Establishment and characterization of HBV-associated B lymphocytes with an immortalization potential

Emerging evidences indicate that hepatitis B virus (HBV) infection is associated with non-Hodgkin lymphoma (NHL), but the mechanisms of HBV-induction lymphomagenesis remain unclear. In this report, retrospective analysis of the prevalence of hepatitis B surface antigen (HBsAg) among NHL cases demonstrated significantly higher HBsAg carrier rate among B-cell NHL cases than controls (other cancers except primary liver cancer) (adjusted odds ratio, 1.56; 95% confidence interval, 1.13–2.16). Furthermore, cells with an immortalization potential existed in the peripheral blood of 4 patients with chronic HBV infection. Characterization of these cells showed their immunophenotypes similar to that of the majority of HBsAg-positive B-cell NHL patients. Immunoglobulin (Ig) gene rearrangements confirmed the clonal Ig gene rearrangements. Cytogenetic analysis revealed abnormal karyotypes of these cells with an immortalization potential. Compared with cells with an immortalization potential that we previously found in B-cell NHL patients by the same way, these cells showed many similar features. In conclusion, cells with an immortalization potential existed in the part of patients with chronic HBV infection before lymphoma development and showed some malignant features. They may be the cellular basis of HBV-associated lymphomagenesis.

Clinicopathologic and molecular features in hairy cell leukemia-variant: single institutional experience

Hairy cell leukemia-variant is rare. Only a small number of cases have been reported in the literature with little cytogenetic or molecular data available. In this study, we describe the clinicopathologic and genetic features of 23 patients with hairy cell leukemia-variant (16 men and 7 women) with a median age of 70 years. Most patients had splenomegaly (90%), leukocytosis (77%), and lymphocytosis (82%); no patients had monocytopenia. Histologically, the bone marrow biopsy specimens showed a mixed pattern of predominantly interstitial and lesser intrasinusoidal infiltration by leukemic cells. In bone marrow aspirate smears most cells had villous cytoplasmic features and a small nucleolus. We describe unusual sites of hairy cell leukemia-variant involvement in 4 patients, including brain, omentum, terminal ileum, and skin at the time of initial presentation. Immunophenotyping showed monotypic B-cells positive for pan B-cell antigens, CD11c, and CD103, and negative for CD25 and annexin A1. Conventional cytogenetic or fluorescence in situ hybridization analysis showed deletions of 17p13/TP53 and 11q22/ATM gene in 5/12 (42%) and 2/9 (22%) cases, respectively. Sequencing of the variable region of IGVH showed mutations (>2% deviation from germline) in 40% of the cases assessed. MAP2K1 mutation (p.C121S) was seen in 1 of 14 (7%) patients tested. No BRAF V600E mutations were detected. The patients were treated in a heterogeneous manner, but most often with therapies designed for classical hairy cell leukemia and the 5-year overall survival was 84%. In summary, hairy cell leukemia-variant exhibits a heterogeneous spectrum of clinical, morphologic, immunophenotypic, and genetic features that may overlap with classic hairy cell leukemia and other hairy cell-like B-cell neoplasms. A subset of patients can have an aggressive clinical course. In our experience MAP2K1 mutations are uncommon in this disease.

Deciphering splenic marginal zone lymphoma pathogenesis: the proposed role of microRNA

Splenic marginal zone lymphoma (SMZL) is a malignancy of mature B-cells that primarily involves the spleen, but can affect peripheral organs as well. Even though SMZL is overall considered an indolent malignancy, the majority of cases will eventually progress to be more aggressive. In recent years, the gene expression profile of SMZL has been characterized in an effort to identify: 1) the etiology of SMZL, 2) biological consequences of SMZL, and 3) putative therapeutic targets. However, due to the vast heterogeneity of the malignancy, no conclusive target(s) have been deciphered. However, the role of miRNA in SMZL, much as it has in chronic lymphocytic leukemia, may serve as a guiding light. As a result, we review the comprehensive expression profiling in SMZL to-date, as well as describe the miRNA (and potential mechanistic roles) that may play a role in SMZL transformation, particularly within the 7q region.

CDK6 Antagonizes p53-Induced Responses during Tumorigenesis

Tumor formation is a multistep process during which cells acquire genetic and epigenetic changes until they reach a fully transformed state. We show that CDK6 contributes to tumor formation by regulating transcriptional responses in a stage-specific manner. In early stages, the CDK6 kinase induces a complex transcriptional program to block p53 in hematopoietic cells. Cells lacking CDK6 kinase function are required to mutate TP53 (encoding p53) to achieve a fully transformed immortalized state. CDK6 binds to the promoters of genes including the p53 antagonists Prmt5, Ppm1d, and Mdm4 The findings are relevant to human patients: Tumors with low levels of CDK6 have mutations in TP53 significantly more often than expected.Significance: CDK6 acts at the interface of p53 and RB by driving cell-cycle progression and antagonizing stress responses. While sensitizing cells to p53-induced cell death, specific inhibition of CDK6 kinase activity may provoke the outgrowth of p53-mutant clones from premalignant cells. Cancer Discov; 8(7); 884-97. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 781.

Del17p does not always significantly influence the survival of B-cell chronic lymphoproliferative disorders

B-cell chronic lymphoproliferative disorders (B-CLPD) comprise several entities with indolent clinical manifestations but heterogeneous survival. Cytogenetic aberrations are now the standard prognostic predictors in chronic lymphocytic leukemia (CLL) but have been less investigated in other subtypes of B-CLPD. In this study, we detected cytogenetic aberrations by fluorescence in situ hybridization (FISH) in 875 B-CLPD patients, based on a panel probes locating at 13q14, 11q22, 17p13 and CEP12. We identified del17p acted as the independent adverse cytogenetic predictor for overall survival (OS) in CLL. Del13q, del11q and del17p were adverse factors for OS in Waldenström's macroglobulinemia in the univariate analysis but lost their role in the multivariate analysis. Trisomy 12 acted as an independent poor factor for both marginal zone lymphoma (MZL) and unclassified B-CLPD (BCLPD-U) subtype. Del17p did not impact survival in MZL and BCLPD-U patients. These contrasting results indicate different roles of the same cytogenetic aberrations in the pathogenesis of each B-CLPD subtype. As del17p contributed to the poorest survival in CLL and desired extraordinary treatment strategy, the imitation of CLL strategy to other B-CLPD with del17p should be carefully advocated based on this study.

Germline large genomic alterations on 7q in patients with multiple primary cancers

Patients with multiple primary cancers (MPCs) are suspected to have a hereditary cancer syndrome. However, only a small proportion may be explained by mutations in high-penetrance genes. We investigate two unrelated MPC patients that met Hereditary Breast and Ovaria Cancer criteria, both presenting triple negative breast tumors and no mutations in BRCA1, BRCA2 and TP53 genes. Germline rearrangements on chromosome 7q, involving over 40 Mb of the same region, were found in both patients: one with mosaic loss (80% of cells) and the other with cnLOH (copy-neutral loss of heterozygosity) secondary to maternal allele duplication. Five children tested had no alterations on 7q. The patients shared 330 genes in common on 7q22.1-q34, including several tumor suppressor genes (TSGs) previously related to breast cancer risk and imprinted genes. The analysis of the triple negative BC from one patient revealed a mosaic gain of 7q translated for over-expressed cancer-related genes. The involvement of TSGs and imprinted genes, mapped on 7q, has the potential of being associated to MPC risk, as well as cancer progression. To our knowledge, this is the first description of patients with MPCs that harbor constitutive large alterations on 7q.

Splenic marginal zone lymphoma

Splenic marginal zone lymphoma (SMZL) is an indolent small B-cell lymphoma involving the spleen and bone marrow characterized by a micronodular tumoral infiltration that replaces the preexisting lymphoid follicles and shows marginal zone differentiation as a distinctive finding. SMZL cases are characterized by prominent splenomegaly and bone marrow and peripheral blood infiltration. Cells in peripheral blood show a villous cytology. Bone marrow and peripheral blood characteristic features usually allow a diagnosis of SMZL to be performed. Mutational spectrum of SMZL identifies specific findings, such as 7q loss and NOTCH2 and KLF2 mutations, both genes related with marginal zone differentiation. There is a striking clinical variability in SMZL cases, dependent of the tumoral load and performance status. Specific molecular markers such as 7q loss, p53 loss/mutation, NOTCH2 and KLF2 mutations have been found to be associated with the clinical variability. Distinction from Monoclonal B-cell lymphocytosis with marginal zone phenotype is still an open issue that requires identification of precise and specific thresholds with clinical meaning.

Molecular pathogenesis of splenic and nodal marginal zone lymphoma

Genomic studies have improved our understanding of the biological basis of splenic (SMZL) and nodal (NMZL) marginal zone lymphoma by providing a comprehensive and unbiased view of the genes/pathways that are deregulated in these diseases. Consistent with the physiological involvement of NOTCH, NF-κB, B-cell receptor and toll-like receptor signaling in mature B-cells differentiation into the marginal zone B-cells, many oncogenic mutations of genes involved in these pathways have been identified in SMZL and NMZL. Beside genetic lesions, also epigenetic and post-transcriptional modifications contribute to the deregulation of marginal zone B-cell differentiation pathways in SMZL and NMZL. This review describes the progress in understanding the molecular mechanism underlying SMZL and NMZL, including molecular and post-transcriptional modifications, and discusses how information gained from these efforts has provided new insights on potential targets of diagnostic, prognostic and therapeutic relevance in SMZL and NMZL.

Lymphoma Heterogeneity: Three Different Histological Pictures and One Unique Clone

We report a patient who developed up to three different lymphomas with the same clonal IGH rearrangement. She was first diagnosed of splenic zone marginal lymphoma and relapsed for the first time with Hodgkin lymphoma histology and later with diffuse large B-cell lymphoma histology. Subsequent biopsies and analysis of clonally rearranged IGH genes helped to elucidate the clonal relationship between the three histologies and to confirm a common origin from the three tissue histologies. An integrated diagnosis should always be performed in order to achieve the most accurate diagnosis and be able to choose the best therapeutic options for our patients.

Splenic marginal zone lymphoma: from genetics to management

Splenic marginal zone lymphoma (SMZL) is a rare B-cell malignancy involving the spleen, bone marrow, and frequently the blood. SMZL lymphomagenesis involves antigen and/or superantigen stimulation and molecular deregulation of genes (NOTCH2 and KLF2) involved in the physiological differentiation of spleen marginal zone B cells. Diagnosis requires either spleen histology or, alternatively, the documentation of a typical cell morphology and immunophenotype on blood cells coupled with the detection of intrasinusoidal infiltration by CD20+ cells in the bone marrow. Among B-cell tumors, deletion of 7q and NOTCH2 mutations are almost specific lesions of SMZL, thus representing promising diagnostic biomarkers of this lymphoma. Although the majority of SMZLs show an indolent course with a median survival of approximately 10 years, nearly 30% of patients experience a poor outcome. No randomized trials are reported for SMZL, and few prospective trials are available. A watch-and-wait approach is advisable for asymptomatic patients. Treatment options for symptomatic patients ranges from splenectomy to rituximab alone or combined with chemotherapy. In some geographic areas, a subset of patients with SMZL associates with hepatitis C virus infection, prompting virus eradication as an effective lymphoma treatment. It would be worthwhile to explore deregulated cellular programs of SMZL as therapeutic targets in the future; improved clinical and biological prognostication will be essential for identifying patients who may benefit from novel approaches.

Genetic aberrations in small B-cell lymphomas and leukemias: molecular pathology, clinical relevance and therapeutic targets

Small B-cell lymphomas and leukemias (SBCLs) are a clinically, morphologically, immunophenotypically and genetically heterogeneous group of clonal lymphoid neoplasms, including entities such as chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), mantle cell lymphoma (MCL), follicular lymphoma (FL), lymphoplasmacytic lymphoma (LPL), marginal zone lymphoma (MZL) and hairy cell leukemia (HCL). The pathogenesis of some of these lymphoid malignancies is characterized by distinct translocations, for example t(11;14) in the majority of cases of MCL and t(14;18) in most cases of FL, whereas other entities are associated with a variety of recurrent but nonspecific numeric chromosomal abnormalities, as exemplified by del(13q14), del(11q22), and +12 in CLL, and yet others such as LPL and HCL that lack recurrent or specific cytogenetic aberrations. The recent surge in next generation sequencing (NGS) technology has shed more light on the genetic landscape of SBCLs through characterization of numerous driver mutations including SF3B1 and NOTCH1 in CLL, ATM and CCND1 in MCL, KMT2D and EPHA7 in FL, MYD88 (L265P) in LPL, KLF2 and NOTCH2 in splenic MZL (SMZL) and BRAF (V600E) in HCL. The identification of distinct genetic lesions not only provides greater insight into the molecular pathogenesis of these disorders but also identifies potential valuable biomarkers for prognostic stratification, as well as specific targets for directed therapy. This review discusses the well-established and recently identified molecular lesions underlying the pathogenesis of SBCLs, highlights their clinical relevance and summarizes novel targeted therapies.

Splenic marginal-zone lymphoma: ontogeny and genetics

Splenic marginal-zone lymphoma (SMZL) is a rare tumor that has recently emerged as a prototype for how the interplay between genetics and environment shapes the natural history of lymphomas. Indeed, the recent identification of molecular immunogenetic subgroups within SMZL may prove to be relevant not only for the sub-classification of the disease but also for improved understanding of the underlying biology. In contrast to other B-cell lymphomas, SMZL lacks a characteristic genetic lesion, although the majority of cases harbor genomic aberrations, as recently revealed by high-throughput studies that identified recurrent genetic aberrations, several in pathways related to marginal-zone differentiation and B-cell signaling. Here we provide an overview of recent research into the molecular and cellular biology of SMZL and related disorders, with special emphasis on immunogenetics and genomic aberrations, and discuss the value of molecular and cellular markers for the diagnosis and differential diagnosis of these entities.

Cytopathology in the diagnosis of lymphoma

FNA is a simple, safe, and an inexpensive sampling technique that plays an important role in the evaluation of lymphadenopathy. The key to enhancing the accuracy of FNA diagnosis of lymphoma is the multi parameter approach in which the cytomorphologic features are evaluated in correlation with the results of ancillary studies and clinical context. A full understanding of the current lymphoma classification, clinical features associated with each lymphoma subtype and the impact of the diagnosis on patient management is essential in FNA diagnosis of lymphoma. It is also important to recognize the limitations of FNA in the primary diagnosis of some subtypes of lymphoma, and tissue biopsy should be recommended for a definitive diagnosis and subclassification in such cases.

Unusual Course of Splenic Marginal Zone Lymphoma

A 53-year-old woman was diagnosed with splenic marginal zone lymphoma by pathological examination on left submandibular lymph node and bone marrow biopsies and markedly enlarged spleen. Four cycles of Rituximab chemotherapy were given. Seven months after finishing Rituximab chemotherapy, she developed left upper extremity swelling without evidence of deep venous thrombosis. Repeat PET/CT scan demonstrated multiple left axillary lymph nodes extending to left retroclavicular region and a new lymph node posterior to the left scapula. Biopsy of the lymph node demonstrated marginal zone lymhoma pattern with increased numbers of large cells, but not outright diffuse large B-cell lymphoma. Despite resuming rituximab, patient had persistent leukocytosis and severe anemia. Restaging PET/CT showed 3 new left anterior cervical lymph nodes and 1 new right axillary lymph node. Spleen has further enlarged. R-CHOP chemotherapy was started, which improved leukocytosis.After 4 cycles of R-CHOP, PET/CT showed new metabolic activity within right inguinal and abdominal lymph nodes. Patient was given one cycle of Bendamustine. She developed a possible “hematoma” in right medial elbow. However, MRI study revealed a subcutaneous deposit of the lymphoma. Patient needs consistently blood transfusion and she deteriorated quickly. Our patient had an aggressive course of splenic marginal zone lymphoma, not responding to four trials of chemotherapy although SMZL is well-known to be an indolent low grade lymphoma. This case report emphasizes the importance to individualize the treatment in SMZL patients and repeat bone marrow biopsy if the disease recurs.

Extranodal and splenic small B-cell lymphoma

Although almost any non-Hodgkin lymphoma can involve the spleen or an extranodal site as part of more widely disseminated disease, there is a group of small B-cell lymphomas that specifically arise in these locations. These are important to recognise as some appear to have a behaviour and prognosis that is distinct from their nodal counterparts. In addition, there are entities that are specific to extranodal locations (such as extranodal marginal zone lymphoma) and to the red or white pulp of the spleen. In this review, the characteristics of these entities will be presented as well as clues to help distinguish lymphoma from reactive infiltrates in extranodal sites and measure to distinguish between small B-cell lymphomas encountered in the spleen and at extranodal locations.

Exon 1 disruption alters tissue-specific expression of mouse p53 and results in selective development of B cell lymphomas

p53 is a tumor suppressor gene mutated in >50% of human cancers, while p53 deficiency in mice results in cancers and accelerated mortality. Thymic T cell lymphoma is the most common malignancy in p53-deficient mice, making it difficult to study the role of p53 in other malignancies. To overcome this limitation, we attempted to generate mice with a reversible p53 knockout (p53^rev/rev) by inserting a floxed transcriptional stop into the first exon of p53, anticipating that this would allow tissue-specific Cre-mediated expression of p53. Contrary to expectations, functional p53 protein was expressed in the thymus and multiple other tissues of p53^rev/rev mice in the absence of Cre, whereas B cells expressed p53 protein only in the presence of B cell-specific CD19-Cre. In the absence of Cre, 76% of p53^rev/rev mice developed splenic marginal zone B cell lymphomas, indicating sensitivity of this B cell subset to transformation caused by p53 deficiency. 5′-RACE identified p53 mRNA transcribed from a novel start site utilized in thymocytes but not normal B cells or B cell lymphomas from p53^rev/rev mice. The p53^rev/rev mouse thus demonstrates an effect of p53 deficiency in development of splenic marginal zone lymphomas and provides a model for study of p53-deficient human B cell lymphomas.

An integrated genomic and expression analysis of 7q deletion in splenic marginal zone lymphoma

Splenic marginal zone lymphoma (SMZL) is an indolent B-cell lymphoproliferative disorder characterised by 7q32 deletion, but the target genes of this deletion remain unknown. In order to elucidate the genetic target of this deletion, we performed an integrative analysis of the genetic, epigenetic, transcriptomic and miRNomic data. High resolution array comparative genomic hybridization of 56 cases of SMZL delineated a minimally deleted region (2.8 Mb) at 7q32, but showed no evidence of any cryptic homozygous deletion or recurrent breakpoint in this region. Integrated transcriptomic analysis confirmed significant under-expression of a number of genes in this region in cases of SMZL with deletion, several of which showed hypermethylation. In addition, a cluster of 8 miRNA in this region showed under-expression in cases with the deletion, and three (miR-182/96/183) were also significantly under-expressed (P<0.05) in SMZL relative to other lymphomas. Genomic sequencing of these miRNA and IRF5, a strong candidate gene, did not show any evidence of somatic mutation in SMZL. These observations provide valuable guidance for further characterisation of 7q deletion.

Whole-genome sequencing identifies recurrent somatic NOTCH2 mutations in splenic marginal zone lymphoma

NOTCH2 mutations in splenic marginal zone lymphoma are associated with poor prognosis.

Splenic marginal zone lymphoma (SMZL), the most common primary lymphoma of spleen, is poorly understood at the genetic level. In this study, using whole-genome DNA sequencing (WGS) and confirmation by Sanger sequencing, we observed mutations identified in several genes not previously known to be recurrently altered in SMZL. In particular, we identified recurrent somatic gain-of-function mutations in NOTCH2, a gene encoding a protein required for marginal zone B cell development, in 25 of 99 (∼25%) cases of SMZL and in 1 of 19 (∼5%) cases of nonsplenic MZLs. These mutations clustered near the C-terminal proline/glutamate/serine/threonine (PEST)-rich domain, resulting in protein truncation or, rarely, were nonsynonymous substitutions affecting the extracellular heterodimerization domain (HD). NOTCH2 mutations were not present in other B cell lymphomas and leukemias, such as chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL; n = 15), mantle cell lymphoma (MCL; n = 15), low-grade follicular lymphoma (FL; n = 44), hairy cell leukemia (HCL; n = 15), and reactive lymphoid hyperplasia (n = 14). NOTCH2 mutations were associated with adverse clinical outcomes (relapse, histological transformation, and/or death) among SMZL patients (P = 0.002). These results suggest that NOTCH2 mutations play a role in the pathogenesis and progression of SMZL and are associated with a poor prognosis.

The coding genome of splenic marginal zone lymphoma: activation of NOTCH2 and other pathways regulating marginal zone development

Splenic marginal zone lymphoma (SMZL) is a B cell malignancy of unknown pathogenesis, and thus an orphan of targeted therapies. By integrating whole-exome sequencing and copy-number analysis, we show that the SMZL exome carries at least 30 nonsilent gene alterations. Mutations in NOTCH2, a gene required for marginal-zone (MZ) B cell development, represent the most frequent lesion in SMZL, accounting for ∼20% of cases. All NOTCH2 mutations are predicted to cause impaired degradation of the NOTCH2 protein by eliminating the C-terminal PEST domain, which is required for proteasomal recruitment. Among indolent B cell lymphoproliferative disorders, NOTCH2 mutations are restricted to SMZL, thus representing a potential diagnostic marker for this lymphoma type. In addition to NOTCH2, other modulators or members of the NOTCH pathway are recurrently targeted by genetic lesions in SMZL; these include NOTCH1, SPEN, and DTX1. We also noted mutations in other signaling pathways normally involved in MZ B cell development, suggesting that deregulation of MZ B cell development pathways plays a role in the pathogenesis of ∼60% SMZL. These findings have direct implications for the treatment of SMZL patients, given the availability of drugs that can target NOTCH, NF-κB, and other pathways deregulated in this disease.

Waldenström macroglobulinemia: a review of the entity and its differential diagnosis

The definition of Waldenström macroglobulinemia (WM), originally described in 1944, has been refined substantially over time. The current fourth edition of the World Health Organization of lymphoid neoplasms, in large part, adopted criteria proposed for WM at a consensus conference in 2002. WM is defined as lymphoplasmacytic lymphoma involving the bone marrow associated with a serum immunoglobulin (Ig) M paraprotein of any concentration. Morphologically, WM is composed of a variable mixture of lymphocytes, plasmacytoid lymphocytes, and plasma cells. Immunophenotypically, the neoplastic cells express monotypic IgM and light chain: B lymphocytes express pan-B-cell antigens and surface Ig are usually negative for CD5 and CD10; and plasma cells are typically positive for CD138, CD38, CD45, cytoplasmic Ig, and CD19 (in a substantial subset of cases). The putative cell of origin of WM is a postantigen selected memory B-cell that has undergone somatic hypermutation. The most common cytogenetic abnormality in WM is del(6q), usually in the region 6q23-24.3, present in 40% to 50% of cases. IGH gene translocations are rare and recurrent chromosomal translocations or gene aberrations have not been identified in WM. Here, we provide a historical perspective of WM, review clinical and pathologic aspects of the disease as it is currently defined, and discuss some practical issues in the differential diagnosis of WM that pathologists encounter in the signout of cases.

BCR and TLR signaling pathways are recurrently targeted by genetic changes in splenic marginal zone lymphomas

The genetics and pathogenesis of splenic marginal zone lymphoma are poorly understood. The lymphoma lacks chromosome translocation, and approximately 30% of cases are featured by 7q deletion, but the gene targeted by the deletion is unknown. A recent study showed inactivation of A20, a "global" NF-κB negative regulator, in 1 of 12 splenic marginal zone lymphomas. To investigate further whether deregulation of the NF-κB pathway plays a role in the pathogenesis of splenic marginal zone lymphoma, we screened several NF-κB regulators for genetic changes by PCR and sequencing. Somatic mutations were found in A20 (6/46=13%), MYD88 (6/46=13%), CARD11 (3/34=8.8%), but not in CD79A, CD79B and ABIN1. Interestingly, these genetic changes are largely mutually exclusive from each other and MYD88 mutation was also mutually exclusive from 7q deletion. These results strongly suggest that deregulation of the TLR (toll like receptor) and BCR (B-cell receptor) signaling pathway may play an important role in the pathogenesis of splenic marginal zone lymphoma.

Molecular characterization of the region 7q22.1 in splenic marginal zone lymphomas

Splenic marginal zone lymphomas (SMZL) are an uncommon type of B-cell non-Hodgkin's lymphoma (NHL-B) in which no specific chromosomal translocations have been described. In contrast, the most frequent cytogenetic abnormality is the loss of the long arm of chromosome 7 (7q). Previous reports have located this loss in the 7q32 region. In order to better characterize the genomic imbalances in SMZL, molecular studies were carried out in 73 patients with SMZL. To gain insight into the mapping at 7q a tiling array was also used. The results confirmed the loss of 7q as the most frequent change. In addition, several abnormalities, including 4q22.1, 1q21.3–q22, 6q25.3, 20q13.33, 3q28, 2q23.3–q24.1 and 17p13, were also present. A loss of 7q22.1 at 99925039–101348479 bp was observed in half of the cases. The region of 7q22.1 has not previously been characterised in SMZL. Our results confirmed the presence of a new region of loss on chromosome 7 in these NHL.

Marginal zone lymphomas with plasmacytic differentiation and related disorders

Marginal zone lymphomas of all types (nodal, splenic, and extranodal mucosa-associated lymphoid tissue [MALT]) may show plasmacytic differentiation. Distinguishing marginal zone lymphomas from other small B-cell lymphomas with plasmacytic differentiation, especially lymphoplasmacytic lymphoma, or from plasma cell neoplasms may be challenging. Marginal zone lymphomas with plasmacytic differentiation were discussed in 2 sessions of the 2009 Society for Hematopathology/European Association for Haematopathology Workshop. Session 4 focused on nodal marginal zone lymphomas, including cases exhibiting classic features and cases displaying atypical phenotypes. The difficulties of classification of cases with increased numbers of large cells were also discussed. Session 5 examined nonnodal marginal zone lymphomas and related entities, including splenic marginal zone lymphoma, MALT lymphoma, γ heavy chain disease, and cryoglobulin-associated lymphoproliferative disorders. These cases illustrate the importance of clinical data and, in some cases, phenotypic and cytogenetic findings in appropriately applying the 2008 World Health Organization criteria.

Splenic marginal zone lymphoma with VH1-02 gene rearrangement expresses poly- and self-reactive antibodies with similar reactivity

One-third of all splenic marginal zone lymphomas (SMZL) use the IgH VH1-02 gene. These cases are usually not associated with hepatitis C virus infection. Of interest, the rearranged VH1-02 genes display similar complementarity determining regions 3, a finding confirmed by our study. The latter suggests that these SMZL may produce antibodies with similar reactivity. We produced recombinant antibodies from 5 SMZL cases with VH1-02 gene rearrangement to study the binding reactivity of these antibodies. Surprisingly, the recombinant antibodies demonstrated poly- and self-reactivity as demonstrated by their reactivity with nuclear, cytoplasmic, as well as membranous antigens expressed by human cells and by reactivity with human serum. This polyreactivity was specific as demonstrated by ELISA. The antibodies did not react with proteins on the cell surface that are induced by apoptosis as shown for antibodies produced by chronic lymphatic leukemia with VH1-02 gene rearrangement. The results indicate that a common subset of SMZL arises from polyreactive B cells, a subset of marginal zone B cells that are important in the immunologic defense against infection.

Employment of oligodeoxynucleotide plus interleukin-2 improves cytogenetic analysis in splenic marginal zone lymphoma

To compare the efficiency of novel mitogenic agents and traditional mitosis inductors, 18 patients with splenic marginal zone lymphoma (SMZL) were studied. Three cultures using oligodeoxynucleotide (ODN) plus interleukin-2 (IL-2), or TPA, or LPS were setup in each patient. Seventeen/18 cases with ODN + IL2 had moderate/good proliferation (94, 4%) as compared with 10/18 cases with TPA and LPS (55%) (P = .015); 14/18 (77, 7%) cases with ODN + IL2 had sufficient good quality of banding as compared with 8/18 cases (44, 4%) with TPA and LPS. The karyotype could be defined from ODN + IL2-stimulated cultures in all 18 patients, 14 of whom (77, 7%) had a cytogenetic aberration, whereas clonal aberrations could be documented in 9 and in 3 cases by stimulation with LPS and TPA, respectively. Recurrent chromosome aberrations in our series were represented by aberrations of chromosome 14q in 5 patients, by trisomy 12 and 7q deletion in 4 cases each, and by abnormalities involving 11q and 13q in two cases each. These findings show that stimulation with ODN + IL2 offers more mitotic figures of better quality and results in an increased rate of clonal aberrations in SMZL, making this method ideal for prospective studies aiming at the definition of the prognostic impact of cytogenetic aberrations in this disorder.

Splenic B-Cell Lymphomas/Leukemias

The diagnosis and classification of lymphoproliferative disorders in the spleen are frequently challenging. While some lymphomas, such as hairy cell leukemia and splenic marginal zone lymphoma, characteristically present with primarily splenic involvement, secondary involvement of the spleen may be seen with any lymphoma. Precise classification requires integration of the morphologic findings with clinical data, phenotypic studies, and often cytogenetic and/or molecular genetic analysis. Correlation with the findings in peripheral blood and bone marrow may also be required in some cases. This article discusses the diagnostic approach to splenic-based lymphoproliferative disorders in routine practice and describes the clinicopathologic features of lymphoid neoplasms that characteristically present in the spleen.

The basis and rational use of molecular genetic testing in mature B-cell lymphomas

An increasing number of neoplasms are associated with variably specific genetic abnormalities. This is best exemplified by hematological malignancies, in which there is a growing list of entities that are defined by their genetic lesion(s); this is not (yet) the case in mature B-cell lymphomas. However, enhanced insights into the pathogenesis of this large and diverse group of lymphomas have emerged with the ongoing unraveling of a plethora of fascinating genetic abnormalities. The purpose of this review is to synthesize well-recognized data and nascent discoveries in our understanding of the genetic basis of a spectrum of mature B-cell lymphomas, and how this may be applied to contemporary clinical practice. Despite the explosion of new and exciting knowledge in this arena, with the potential for enhanced diagnostic and prognostic strategies, it is essential to remain cognizant of the limitations (and complexity) of genetic investigations, so that assays can be developed and used both judiciously and rationally.