Performance of a Commercially Available MAL Antibody in the Diagnosis of Primary Mediastinal Large B-Cell Lymphoma

Diffuse large B-cell lymphoma presenting with pulmonary artery compression symptoms, case reports

Mediastinal diffuse large B-cell lymphoma (DLBC) may manifest in different presentations including systemic symptoms and local mass symptoms. We report two cases of diffuse large B-cell lymphoma presenting with pulmonary artery compression symptoms. The first case is of a 38-year-old Asian man which mimicked pulmonary embolism, and the second one is of a 27-year-old Asian woman who presented with fainting and respiratory symptoms due to local mass effect. Both cases were significantly improved after treatment. Local mass effect symptoms may be the first clinical presentation in DLBC lymphoma and should not be overlooked.

Mediastinal large B cell lymphoma and surrounding gray areas: a report of the lymphoma workshop of the 20th meeting of the European Association for Haematopathology

Session 3 of the 2021 European Association for Haematopathology/Society for Hematopathology Workshop focused on mediastinal large B cell lymphomas and surrounding gray areas. One half of the session was dedicated to primary mediastinal large B cell lymphoma (PMBL) and included cases with classic clinicopathologic features, as well as cases with either morphologic or immunophenotypic variation, and PMBL-like cases with primary extramediastinal disease. The role of additional immunophenotyping and/or molecular testing to aid in the diagnosis of PMBL was discussed. The second half of the session focused on mediastinal and non-mediastinal gray zone lymphomas (GZL) with features intermediate between diffuse large B cell lymphoma (DLBCL) and classic Hodgkin lymphoma (CHL). Several cases illustrating the current challenges in separating this entity from PMBL/DLBCL and CHL were presented. There was discussion regarding the clinical and genetic differences between mediastinal and non-mediastinal GZLs. Rare cases of PMBL and GZL associated with EBV or follicular lymphoma were reviewed. Finally, several cases included in the session highlighted composite or sequential CHL and PMBL/DLBCL and/or GZL, highlighting challenges in separating such cases from GZL.

Updates in the Management of Primary Mediastinal B Cell Lymphoma

Primary mediastinal B cell lymphoma (PMBCL) is considered a distinct pathology according to the WHO classification of lymphoid malignancies. Patients have a better prognosis after the addition of Rituximab to anthracycline-based chemotherapy. The role of consolidative radiotherapy is controversial after the approval of dose-adjusted R-EPOCH and the selection of patients to undergo radiotherapy is based on end-of-therapy PET CT. In the relapsed/refractory setting, new approved drugs and other under investigation have improved patient outcomes. This review summarizes the different treatment modalities in (PMBCL) in the frontline and the relapsed/refractory settings.

Clostridium perfringens Epsilon Toxin Binds to and Kills Primary Human Lymphocytes

Clostridium perfringens epsilon toxin (ETX) is the third most lethal bacterial toxin and has been suggested to be an environmental trigger of multiple sclerosis, an immune-mediated disease of the human central nervous system. However, ETX cytotoxicity on primary human cells has not been investigated. In this article, we demonstrate that ETX preferentially binds to and kills human lymphocytes expressing increased levels of the myelin and lymphocyte protein MAL. Using flow cytometry, ETX binding was determined to be time and dose dependent and was highest for CD4+ cells, followed by CD8+ and then CD19+ cells. Similar results were seen with ETX-induced cytotoxicity. To determine if ETX preference for CD4+ cells was related to MAL expression, MAL gene expression was determined by RT-qPCR. CD4+ cells had the highest amount of Mal gene expression followed by CD8+ and CD19+ cells. These data indicate that primary human cells are susceptible to ETX and support the hypothesis that MAL is a main receptor for ETX. Interestingly, ETX bindings to human lymphocytes suggest that ETX may influence immune response in multiple sclerosis.

Hodgkin Lymphoma and Its Differential Diagnosis: New Twists on an Old Challenge

Hodgkin lymphoma is a B-cell neoplasm that typically presents with localized, nodal disease. Tissues are characterized by few large neoplastic cells, usually comprising less than 10% of tissue cellularity, present in a background of abundant nonneoplastic inflammatory cells. This inflammatory microenvironment, although key to the pathogenesis, can make diagnosis a challenge because reactive conditions, lymphoproliferative diseases, and other lymphoid neoplasms may mimic Hodgkin lymphoma and vice versa. This review provides an overview of the classification of Hodgkin lymphoma, its differential diagnosis, including emerging and recently recognized entities, and strategies to resolve challenging dilemmas and avoid diagnostic pitfalls.

Large B-Cell Lymphomas in the 5th Edition of the WHO-Classification of Haematolymphoid Neoplasms-Updated Classification and New Concepts

The family/class of the large B-cell lymphomas (LBCL) in the 5th edition of the World Health Organization (WHO) classification of haematolymphoid tumors (WHO-HAEM5) features only a few major changes as compared to the 4th edition. In most entities, there are only subtle changes, many of them only representing some minor modifications in diagnostic terms. Major changes have been made in the diffuse large B-cell lymphomas (DLBCL)/high-grade B-cell lymphomas (HGBL) associated with MYC and BCL2 and/or BCL6 rearrangements. This category now consists of MYC and BCL2 rearranged cases exclusively, while the MYC/BCL6 double hit lymphomas now constitute genetic subtypes of DLBCL, not otherwise specified (NOS) or of HGBL, NOS. Other major changes are the conceptual merger of lymphomas arising in immune-privileged sites and the description of LBCL arising in the setting of immune dysregulation/deficiency. In addition, novel findings concerning underlying biological mechanisms in the pathogenesis of the different entities are provided.

Primary mediastinal Large B-cell Lymphoma

Primary mediastinal large B-cell lymphoma (PMBCL) is a separate entity in the WHO classification based on clinico-pathologic features and a distinct molecular signature which overlaps with nodular sclerosis classical Hodgkin lymphoma (NScHL). Molecular classifiers can distinguish PMBCL from diffuse large B-cell lymphoma (DLBCL) using RNA derived from paraffin-embedded tissue and are integral to future studies. However, given that ~5% of DLBCL can have a 'molecular' PMBCL phenotype in the absence of mediastinal involvement, clinical information will remain critical for diagnosis. Studies over the last 10-20 years have elucidated the biologic hallmarks of PMBCL which are reminiscent of cHL, including the importance of JAK-STAT and NFKB signaling pathways as well as an immune evasion phenotype through multiple converging genetic aberrations. The outcome of PMBCL has improved in the modern rituximab era, however controversies remain whether there is a single standard treatment for all patients and when to integrate radiotherapy. Regardless of the frontline therapy, refractory disease can occur in up to 10% of patients and correlates with poor outcome. With emerging data supporting high efficacy of PD1 inhibitors in PMBCL, studies are underway integrating them into the up-front setting.

How I Diagnose Primary Mediastinal (Thymic) Large B-Cell Lymphoma

OBJECTIVES

Primary mediastinal (thymic) large B-cell lymphoma (PMBL) is an uncommon large B-cell neoplasm recognized by the World Health Organization as a distinct entity on the basis of its unique clinical features, histogenesis, phenotype, and pathogenetic mechanisms. The diagnosis of PMBL can be challenging because of features that may overlap with other (Hodgkin and non-Hodgkin) lymphoma types. This review describes our approach to the diagnosis of PMBL.

METHODS

Two cases are presented to illustrate how we diagnose PMBL and separate PMBL from related histologic and biological mimickers, such as Hodgkin lymphoma and gray zone lymphoma.

RESULTS

A diagnosis of PMBL requires correlation of morphology and immunophenotype with clinical and staging data. Gene expression analysis is not typically performed in clinical labs but has expanded our understanding of the functional pathways underlying this disease and helped identify biomarkers that can be translated to diagnostic practice and possibly to future therapeutic options.

CONCLUSIONS

PMBL and closely related entities can pose diagnostic challenges. It is important to understand the borders between PMBL and other closely related lymphoma types so that patients receive successful primary treatment with curative intent.

Mediastinal Lymphoproliferative Disorders

Lymphoproliferative disorders comprise 50% to 60% of all mediastinal malignancies in both children and adults. Primary mediastinal involvement is rare (∼5%), whereas secondary mediastinal involvement by systemic disease is more common (10% to 25%). Primary mediastinal disease is defined as involvement by a lymphoproliferative disorder of mediastinal lymph nodes, the thymus, and/or extranodal mediastinal organs without evidence of systemic disease at presentation. In this review, the clinical, radiologic, histopathologic, immunohistochemical, and genetic features of some of the most characteristic mediastinal lymphoproliferative disorders are presented. The entities discussed here include: classic Hodgkin lymphoma with emphasis on nodular sclerosis and mixed cellularity types, and non-Hodgkin lymphomas, including primary mediastinal (thymic) large B-cell lymphoma, mediastinal gray zone lymphoma, mediastinal diffuse large B-cell lymphoma, thymic marginal zone lymphoma, mediastinal plasmacytoma, T-lymphoblastic lymphoma, and anaplastic large cell lymphoma. Although not a malignant process, hyaline vascular Castleman disease is also discussed here as this disorder commonly involves the mediastinum. Despite multiple advances in hematopathology in recent decades, the day-to-day diagnosis of these lesions still requires a morphologic approach and a proper selection of immunohistochemical markers. For this reason, it is crucial for general pathologists to be familiar with these entities and their particular clinicoradiologic presentation.

Characterization of DLBCL with a PMBL gene expression signature

Primary mediastinal large B-cell lymphoma (PMBL) is a type of aggressive B-cell lymphoma that typically affects young adults, characterized by presence of a bulky anterior mediastinal mass. Lymphomas with gene expression features of PMBL have been described in nonmediastinal sites, raising questions about how these tumors should be classified. Here, we investigated whether these nonmediastinal lymphomas are indeed PMBLs or instead represent a distinct group within diffuse large B-cell lymphoma (DLBCL). From a cohort of 325 de novo DLBCL cases, we identified tumors from patients without evidence of anterior mediastinal involvement that expressed a PMBL expression signature (nm-PMBLsig+; n = 16; 5%). A majority of these tumors expressed MAL and CD23, proteins typically observed in bona fide PMBL (bf-PMBL). Evaluation of clinical features of nm-PMBLsig+ cases revealed close associations with DLBCL, and a majority displayed a germinal center B cell-like cell of origin (GCB). In contrast to patients with bf-PMBL, patients with nm-PMBLsig+ presented at an older age and did not show pleural disease, and bone/bone marrow involvement was observed in 3 cases. However, although clinically distinct from bf-PMBL, nm-PMBLsig+ tumors resembled bf-PMBL at the molecular level, with upregulation of immune response, JAK-STAT, and NF-κB signatures. Mutational analysis revealed frequent somatic gene mutations in SOCS1, IL4R, ITPKB, and STAT6, as well as CD83 and BIRC3, with the latter genes significantly more frequently affected than in GCB DLBCL or bf-PMBL. Our data establish nm-PMBLsig+ lymphomas as a group within DLBCL with distinct phenotypic and genetic features. These findings may have implications for gene expression- and mutation-based subtyping of aggressive B-cell lymphomas and related targeted therapies.

Immunohistochemistry with anti-MAL antibody and RNAscope with MAL probes are complementary techniques for diagnosis of primary mediastinal large B-cell lymphoma

AIMS

Primary mediastinal large B-cell lymphoma (PMBL) diagnosis can be challenging on needle biopsies. Robust techniques are needed to ensure diagnosis of this lymphoma which is highly sensitive to recently developed therapy protocols.

METHODS

In this study, we sought to determine precise PMBL phenotype, compared with diffuse large B-cell lymphoma not otherwise specified, by combining immunohistochemistry with anti-MAL antibody and RNA in situ hybridisation (RNAscope) with specific MAL probes.

RESULTS

The overall MAL positivity level reached 93% (14/15) of cases of PMBL. Among the 15 cases enrolled in the study, 11 were undoubtedly positive for MAL immunostaining whereas 13 were positive by RNA in situ hybridisation. Interestingly, one case that was negative by in situ hybridisation turned out to be positive by immunohistochemistry.

CONCLUSIONS

Taken together, our results demonstrate that in situ detection of both MAL transcripts and protein are complementary and increase the sensitivity and specificity of PMBL diagnosis.

Diffuse large B-cell lymphoma variants: an update

Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma, representing approximately one-third of all cases worldwide. In the World Health Organization (WHO) classification of lymphomas, most cases of DLBCL are designated as not otherwise specified (NOS). About 20% of cases, however, are designated as specific variants of DLBCL. These variants, 13 in total, are specified on the basis of distinctive morphological or immunophenotypic findings or distinctive biological or clinical issues associated with their diagnoses. In this review we discuss the following variants: T-cell/histiocyte-rich large B-cell lymphoma; ALK-positive large B-cell lymphoma; plasmablastic lymphoma; intravascular large B-cell lymphoma; large B-cell lymphoma with IRF4 rearrangement; primary mediastinal large B-cell lymphoma; primary cutaneous diffuse large B-cell lymphoma, leg type; primary diffuse large B-cell lymphoma of the central nervous system; diffuse large B-cell lymphoma associated with chronic inflammation; lymphomatoid granulomatosis; primary effusion lymphoma; and HHV8-positive diffuse large B-cell lymphoma, NOS. Two additional variants recognised in the WHO classification, EBV-positive diffuse large B-cell lymphoma and EBV-positive mucocutaneous ulcer are discussed elsewhere in another review within this issue of Pathology. Although not recognised as a specific variant in the current WHO classification, primary testicular diffuse large B-cell lymphoma also has unique biological features and requires some modification of the standard treatment approach for patients with DLBCL. Therefore, we suggest that primary testicular diffuse large B-cell lymphoma also should be recognised as a specific variant of DLBCL in a future version of the WHO classification.

Primary Mediastinal Nodal and Extranodal Non-Hodgkin Lymphomas: Current Concepts, Historical Evolution, and Useful Diagnostic Approach: Part 1

Primary mediastinal non-Hodgkin lymphomas (PM-NHLs) represent ~5% of all NHLs and comprise lymphomas of B-cell and T-cell origin. PM-NHLs are defined as involvement of mediastinal lymph nodes, thymus, and/or mediastinal organs (heart, lung, pleura, pericardium) by NHL without evidence of systemic disease at presentation. The clinical scenario is variable and depends on the lymphoma subtype. The radiologic presentation is also variable ranging from a mediastinal mass with or without superior vena cava syndrome, a pleural or a cardiac mass associated with an effusion, or as an effusion only. The diagnosis of PM-NHLs can only be established by microscopic evaluation, and therefore, general pathologists should be aware of these tumors and familiar with their diagnostic approach. The most common anterior mediastinal NHLs (90% to 95%) are primary mediastinal large B-cell lymphoma and T lymphoblastic lymphoma. Thymic marginal zone lymphoma and mediastinal gray zone lymphoma are very rare. The remainder PM-NHLs involving middle or posterior mediastinum include diffuse large B-cell lymphoma (DLBCL) and rare cases of T-cell lymphoma, including anaplastic large cell lymphoma and breast implant-associated anaplastic large cell lymphoma extending to the anterior mediastinum. Primary pleural and cardiac NHLs are mostly DLBCLs. Other rare subtypes of PM-NHLs include DLBCL associated with chronic inflammation/pyothorax-associated lymphoma, fibrin-associated DLBCL (both EBV), and pleural and/or pericardial primary effusion lymphoma (HHV-8/EBV). We review the historical aspects, epidemiology, clinico-radiologic features, histopathology, immunohistochemistry, differential diagnosis, and relevant cytogenetic and molecular features of PM (thymic) LBCL, PM "nonthymic" DLBCL, BCL, unclassifiable, with features intermediate between DLBCL and classic Hodgkin lymphoma (mediastinal gray zone lymphoma), DLBCL associated with chronic inflammation (pyothorax-associated lymphoma), fibrin-associated DLBCL, and primary effusion lymphoma. This review represents the first part of 2 manuscripts covering PM-NHLs.

Molecular Genetics in the Diagnosis and Biology of Lymphoid Neoplasms

OBJECTIVES

The 2017 Workshop of the Society for Hematopathology/European Association for Haematopathology reviewed the role of molecular genetics in the diagnosis and biology of lymphoid neoplasms.

METHODS

The Workshop Panel reviewed 82 cases.

RESULTS

Molecular genetic testing reveals alterations that expand the spectrum of diseases such as DUSP22 rearrangement in ALK-negative anaplastic large cell lymphoma, large B-cell lymphoma with IRF4 rearrangement, MYD88 mutations in B-cell lymphomas, Burkitt-like lymphoma with 11q aberrations, and diagnostic criteria for high-grade B-cell lymphomas. Therapeutic agents and natural tumor progression may be associated with transcriptional reprogramming that lead to transdifferentiation and lineage switch.

CONCLUSIONS

Application of emerging technical advances has revealed the complexity of genetic events in lymphomagenesis, progression, and acquired resistance to therapies. They also contribute to enhanced understanding of the biology of indolent vs aggressive behavior, clonal evolution, tumor progression, and transcriptional reprogramming associated with transdifferentiation events that may occur subsequent to therapy.

Cytologic perspectives on neoteric B-cell lymphoproliferative disorders

The 2008 World Health Organization (WHO) classification of hematopoietic and lymphoid tissues has been recently revised, and publication of the updated 2016 version is expected soon. Given that cytopathologists are often involved in the diagnosis of primary, recurrent, and transformed lymphoproliferative disorders, knowledge of updates to the WHO lymphoma classification, including terminology, pathogenesis, ancillary techniques, and targeted therapies is necessary. Herein, we reference the last decade of cytology specific literature for seven newer B-cell disorders and provide illustrative examples of each entity from our files.