Characterization of a variant of t(14;18) negative nodal diffuse follicular lymphoma with CD23 expression, 1p36/TNFRSF14 abnormalities, and STAT6 mutations

The fifth edition of the WHO classification of mature B-cell neoplasms: open questions for research

The fifth edition of the World Health Organization Classification of Haematolymphoid Tumours (WHO-HAEM5) is the product of an evidence-based evolution of the revised fourth edition with wide multidisciplinary consultation. Nonetheless, while every classification incorporates scientific advances and aims to improve upon the prior version, medical knowledge remains incomplete and individual neoplasms may not be easily subclassified in a given scheme. Thus, optimal classification requires ongoing study, and there are certain aspects of some entities and subtypes that require further refinements. In this review, we highlight a selection of these challenging areas to prompt more research investigations. These include (1) a 'placeholder term' of splenic B-cell lymphoma/leukaemia with prominent nucleoli (SBLPN) to accommodate many of the splenic lymphomas previously classified as hairy cell leukaemia variant and B-prolymphocytic leukaemia, a clear new start to define their pathobiology; (2) how best to classify BCL2 rearrangement negative follicular lymphoma including those with BCL6 rearrangement, integrating the emerging new knowledge on various germinal centre B-cell subsets; (3) what is the spectrum of non-IG gene partners of MYC translocation in diffuse large B-cell lymphoma/high-grade B-cell lymphoma and how they impact MYC expression and clinical outcome; how best to investigate this in a routine clinical setting; and (4) how best to define high-grade B-cell lymphoma not otherwise specified and high-grade B-cell lymphoma with 11q aberrations to distinguish them from their mimics and characterise their molecular pathogenetic mechanism. Addressing these questions would provide more robust evidence to better define these entities/subtypes, improve their diagnosis and/or prognostic stratification, leading to better patient care. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

[CD23 positive, BCL2 rearrangement-negative germinal centre lymphomas]

Acknowledgeing that the group of follicular lymphomas is to be regarded as very heterogeneous, a group of follicular lymphomas has been delineated in recent years that was characterised by an often diffuse growth (without formation of evident follicular structures) as well as expression of CD23 in the lymphoma cells and the absence of the classic BCL2 translocation. Further characteristics are a preferred inguinal localisation of the lymphomas and a localised stage with a good prognosis. Genetically, this lymphoma group is characterised by a high rate of either STAT6 or SOCS1 mutations.The ICC classification took this development into account by introducing the provisional entity CD23 positive, BCL2 rearrangement-negative germinal centre lymphoma. Further studies must now show how exactly this entity can be defined (combination of morphology, immunohistochemical phenotype, focus on genetic alterations) in order to pave the way towards a uniform classification and a better clinical characterisation of these cases - especially with regard to possible new therapeutic treatment options.

Oral follicular lymphoma: a clinicopathologic and molecular study

Follicular lymphoma is a hematolymphoid neoplasm that originates from germinal center B cells. It is made up of a combination of small cleaved centrocytes and a varying quantity of larger non-cleaved centroblasts to describe the clinical, microscopic, immunohistochemical, and molecular features of oral follicular lymphomas. Follicular lymphomas affecting the oral cavity were retrieved from pathology files. Immunohistochemistry was performed to confirm the diagnosis, and fluorescence in situ hybridization (FISH) was employed to detect rearrangements in BCL2, BCL6, and MYC genes. Clinical and follow-up data were obtained from the patient's medical and pathology files. Twenty cases were obtained. There was an equal sex distribution (10 males: 10 females) and a mean age of 60.9 years (range: 10-83 years-old). Lesions presented as asymptomatic swellings, usually in the palate (10 cases) and the buccal mucosa (7 cases). Five patients presented with concomitant nodal involvement. Microscopic evaluation depicted the follicular growth pattern with diffuse areas in six cases. Grades 1 and 2 follicular lymphomas represented 12 cases, while grade 3A neoplasms accounted for other 8 cases. Two cases showed rearrangements in MYC, BCL2, and BCL6 genes, while single BCL2 translocation was found in eight cases. Two cases had no translocation. Three patients deceased and the 2-year overall survival achieved 88%. Follicular lymphoma affecting the oral cavity is uncommon, usually affects the palate as a non-ulcerated swelling and the presence of a systemic disease most always be ruled out.

Cytogenomics of B-cell non-Hodgkin lymphomas: The "old" meets the "new"

For the routine diagnosis of haematological neoplasms an integrative approach is used considering the morphology, and the immunophenotypic, and molecular features of the tumor sample, along with clinical information. The identification and characterization of recurrent chromosomal aberrations mainly detected by conventional and molecular cytogenetics in the tumor cells has a major impact on the classification of lymphoid neoplasms. Some of the B-cell non-Hodgkin lymphomas are characterized by particular chromosomal aberrations, highlighting the relevance of conventional and molecular cytogenetic studies in their diagnosis and prognosis. In the current genomics era, next generation sequencing provides relevant information as the mutational profiles of haematological malignancies, improving their classification and also the clinical management of the patients. In addition, other new technologies have emerged recently, such as the optical genome mapping, which can overcome some of the limitations of conventional and molecular cytogenetics and may become more widely used in the cytogenetic laboratories in the upcoming years. Moreover, epigenetic alterations may complement genetic changes for a deeper understanding of the pathogenesis underlying B-cell neoplasms and a more precise risk-based patient stratification. Overall, here we describe the current state of the genomic data integrating chromosomal rearrangements, copy number alterations, and somatic variants, as well as a succinct overview of epigenomic changes, which altogether constitute a comprehensive diagnostic approach in B-cell non-Hodgkin lymphomas.

Cytogenetics in the management of mature B-cell non-Hodgkin lymphomas: Guidelines from the Groupe Francophone de Cytogénétique Hematologique (GFCH)

Non-Hodgkin lymphomas (NHL) consist of a wide range of clinically, phenotypically and genetically distinct neoplasms. The accurate diagnosis of mature B-cell non-Hodgkin lymphoma relies on a multidisciplinary approach that integrates morphological, phenotypical and genetic characteristics together with clinical features. Cytogenetic analyses remain an essential part of the diagnostic workup for mature B-cell lymphomas. Karyotyping is particularly useful to identify hallmark translocations, typical cytogenetic signatures as well as complex karyotypes, all bringing valuable diagnostic and/or prognostic information. Besides the well-known recurrent chromosomal abnormalities such as, for example, t(14;18)(q32;q21)/IGH::BCL2 in follicular lymphoma, recent evidences support a prognostic significance of complex karyotype in mantle cell lymphoma and Waldenström macroglobulinemia. Fluorescence In Situ Hybridization is also a key analysis playing a central role in disease identification, especially in genetically-defined entities, but also in predicting transformation risk or prognostication. This can be exemplified by the pivotal role of MYC, BCL2 and/or BCL6 rearrangements in the diagnostic of aggressive or large B-cell lymphomas. This work relies on the World Health Organization and the International Consensus Classification of hematolymphoid tumors together with the recent cytogenetic advances. Here, we review the various chromosomal abnormalities that delineate well-established mature B-cell non-Hodgkin lymphoma entities as well as newly recognized genetic subtypes and provide cytogenetic guidelines for the diagnostic management of mature B-cell lymphomas.

The pathobiology of follicular lymphoma

Follicular lymphoma is one of the most frequent lymphomas. Histologically, it is characterized by a follicular (nodular) growth pattern of centrocytes and centroblasts; mixed with variable immune microenvironment cells. Clinically, it is characterized by diffuse lymphadenopathy, bone marrow involvement, and splenomegaly. It is biologically and clinically heterogeneous. In most patients it is indolent, but others have a more aggressive evolution with relapses; and transformation to diffuse large B-cell lymphoma. Tumorigenesis includes an asymptomatic preclinical phase in which premalignant B-lymphocytes with the t(14;18) chromosomal translocation acquire additional genetic alterations in the germinal centers, and clonal evolution occurs, although not all the cells progress to the tumor stage. This manuscript reviews the pathobiology and clinicopathological characteristics of follicular lymphoma. It includes a description of the physiology of the germinal center, the genetic alterations of BCL2 and BCL6, the mutational profile, the immune checkpoint, precision medicine, and highlights in the lymphoma classification. In addition, a comment and review on artificial intelligence and machine (deep) learning are made.

The clinical and molecular taxonomy of t(14;18)-negative follicular lymphomas

Follicular lymphoma (FL) is a neoplasm derived from germinal center B cells, composed of centrocytes and centroblasts, with at least a focal follicular growth pattern. The t(14;18) translocation together with epigenetic deregulation through recurrent genetic alterations are now recognized as the hallmark of FL. Nevertheless, FL is a heterogeneous disease, clinically, morphologically, and biologically. The existence of FL lacking the t(14;18) chromosomal alteration highlights the complex pathogenesis of FL, and indicates that there are alternative pathogenetic mechanisms that can induce a neoplasm with follicular center B-cell phenotype. Based on their clinical presentation, t(14;18)-negative FLs can be divided into 3 broad groups: nodal presentation, extranodal presentation, and those affecting predominantly children and young adults. Recent studies have shed some light into the genetic alterations of t(14;18)-negative FL. Within the group of t(14;18)-negative FL with nodal presentation, cases with STAT6 mutations are increasingly recognized as a distinctive molecular subgroup, often cooccurring with CREBBP and/or TNFRSF14 mutations. FL with BCL6 rearrangement shows clinicopathological similarities to its t(14;18)-positive counterpart. In contrast, t(14;18)-negative FL in extranodal sites is characterized mainly by TNFRSF14 mutations in the absence of chromatin modifying gene mutations. FL in children have a unique molecular landscape when compared with those in adults. Pediatric-type FL (PTFL) is characterized by MAP2K1, TNFRSF14, and/or IRF8 mutations, whereas large B-cell lymphoma with IRF4 rearrangement is now recognized as a distinct entity, different from PTFL. Ultimately, a better understanding of FL biology and heterogeneity should help to understand the clinical differences and help guide patient management and treatment decisions.

Personalised therapy in follicular lymphoma - is the dial turning?

Follicular lymphoma is the most common indolent lymphoma accounting for approximately 20%-25% of all new non-Hodgkin lymphoma diagnoses in western countries. Whilst outcomes are mostly favorable, the spectrum of clinical phenotypes includes high-risk groups with significantly inferior outcomes. This review discusses recent updates in risk stratification and treatment approaches from upfront treatment for limited and advanced stage follicular lymphoma to the growing options for relapsed, refractory disease with perspectives on how to approach this from a personalized lens. Notable gaps remain on how one can precisely and prospectively select optimal treatment for patients based on varying risks, with an anticipation that an increased understanding of the biology of these different phenotypes and increasing refinement of imaging- and biomarker-based tools will, in time, allow these gaps to be closed.

[Classification of indolent B-cell lymphomas : Novelties and open questions]

The 5th edition of the WHO classification (WHO-HAEM5) and the International Consensus Classification (ICC) have considerable overlap but also some distinct differences in categorizing indolent B‑cell lymphomas. Most differences with the expected impact on the daily diagnostic routine relate to follicular lymphoma (FL). Grading of FL remains mandatory only in the ICC; a diffuse growth pattern in an FL with > 15 blasts per high-power field (FL grade 3A) is not automatically classified as DLBCL according to WHO-HAEM5, and an FL subtype with unusual morphology (blastoid or large centrocyte) and biology is recognized as an entity only in the WHO-HAEM5. With the exception of B‑prolymphocytic leukemia, which is no longer acknowledged in WHO-HAEM5, there are only minor differences between both classifications and include updated names of entities, improved diagnostic criteria, and upgrades from provisional to definite entities.

Follicular Lymphoma in the 5th Edition of the WHO-Classification of Haematolymphoid Neoplasms-Updated Classification and New Biological Data

The conceptual description of Follicular lymphoma (FL) in the 5th edition of the World Health Organization (WHO) classification of haematolymphoid tumors (WHO-HAEM5) has undergone significant revision. The vast majority of FL (85%) with a follicular growth pattern are composed of centrocytes and centroblasts, harbor the t(14;18)(q32;q21) translocation and are now termed classic FL (cFL). They are set apart from three related subtypes, FL with predominantly follicular growth pattern, FL with unusual cytological features (uFL) and follicular large B-cell lymphoma (FLBCL). In contrast to the revised 4th edition of the WHO classification of haematolymphoid tumors (WHO-HAEM4R), grading of cFL is no longer mandatory. FL with a predominantly diffuse growth pattern had been previously recognized in WHO-HAEM4R. It frequently occurs as a large tumor in the inguinal region and is associated with CD23 expression. An absence of the IGH::BCL2 fusion and frequent STAT6 mutations along with 1p36 deletion or TNFRSF14 mutation is typical. The newly introduced subtype of uFL includes two subsets that significantly diverge from cFL: one with "blastoid" and one with "large centrocyte" variant cytological features. uFL more frequently displays variant immunophenotypic and genotypic features. FLBCL is largely identical to WHO-HAEM4R FL grade 3B and renaming was done for reasons of consistency throughout the classification. In-situ follicular B-cell neoplasm, pediatric-type FL, duodenal-type FL and primary cutaneous follicle center lymphoma are categorized as discrete entities. In addition, novel findings concerning underlying biological mechanisms in the pathogenesis of early and systemic follicular lymphoma will be presented.

Follicular lymphoma and marginal zone lymphoma: how many diseases?

Follicular lymphoma (FL) and marginal zone lymphoma (MZL) are indolent mature B-cell neoplasms with variable clinical presentation and distinct histopathologic features. Recent advances in the biology and molecular characteristics of these lymphomas have further expanded our understanding of the heterogeneous nature of these lymphomas, with increasing recognition of specific disease entities within the broader categories of FL and MZL. Here, we discuss the conclusions of the 2022 International Consensus Classification of Mature Lymphoid Neoplasms (2022 ICC) dealing with FL, and review differences with the proposed WHO 5th Edition classification. We review issues related to grading and alternative forms of FL especially those lacking the genetic hallmark of FL, the t(14;18) chromosomal alteration. Among them, t(14;18)-negative CD23⁺ follicle center lymphoma has been proposed by the 2022 ICC as a provisional entity. Other follicle center-derived lymphomas such as pediatric-type follicular lymphoma, testicular follicular lymphoma, primary cutaneous follicle center lymphoma, and large B-cell lymphoma with IRF4 rearrangement are considered distinct entities separate from conventional FL. Importantly, large B-cell lymphoma with IRF4 rearrangement introduced as a provisional entity in the WHO 2017 is upgraded to a definite entity in the 2022 ICC. We also discuss diagnostic strategies for recognition of MZLs including splenic MZL, extranodal MZL (MALT lymphoma), and primary nodal MZL. The importance of molecular studies in the distinction among marginal zone lymphoma subtypes is emphasized, as well as their value in the differential diagnosis with other B-cell lymphomas.

A comparison of the International Consensus and 5th World Health Organization classifications of mature B-cell lymphomas

Several editions of the World Health Organization (WHO) classifications of lympho-hemopoietic neoplasms in 2001, 2008 and 2017 served as the international standard for diagnosis. Since the 4th WHO edition, here referred as WHO-HAEM4, significant clinico-pathological, immunophenotypic and molecular advances have been made in the field of lymphomas, contributing to refining diagnostic criteria of several diseases, to upgrade entities previously defined as provisional and to identify new entities. This process has resulted in two recent classifying proposals of lymphoid neoplasms, the International Consensus Classification (ICC) and the 5th edition of the WHO classification (WHO-HAEM5). In this paper, we review and compare the two classifications in terms of diagnostic criteria and entity definition, with focus on mature B-cell neoplasms. The main aim is to provide a tool to facilitate the work of pathologists, hematologists and researchers involved in the diagnosis and treatment of lymphomas.

Molecular subclusters of follicular lymphoma: a report from the United Kingdom's Haematological Malignancy Research Network

Follicular lymphoma (FL) is morphologically and clinically diverse, with mutations in epigenetic regulators alongside t(14;18) identified as disease-initiating events. Identification of additional mutational entities confirms this cancer's heterogeneity, but whether mutational data can be resolved into mechanistically distinct subsets remains an open question. Targeted sequencing was applied to an unselected population-based FL cohort (n = 548) with full clinical follow-up (n = 538), which included 96 diffuse large B-cell lymphoma (DLBCL) transformations. We investigated whether molecular subclusters of FL can be identified and whether mutational data provide predictive information relating to transformation. DNA extracted from FL samples was sequenced with a 293-gene panel representing genes frequently mutated in DLBCL and FL. Three clusters were resolved using mutational data alone, independent of translocation status: FL_aSHM, with high burden of aberrant somatic hypermutation (aSHM) targets; FL_STAT6, with high STAT6 & CREBBP mutation and low aSHM; and FL_Com, with the absence of features of other subtypes and enriched KMT2D mutation. Analysis of mutation signatures demonstrated differential enrichment of predicted mutation signatures between subgroups and a dominant preference in the FL_aSHM subgroup for G(C>T)T and G(C>T)C transitions consistent with previously defined aSHM-like patterns. Of transformed cases with paired samples, 17 of 26 had evidence of branching evolution. Poorer overall survival (OS) in the aSHM group (P = .04) was associated with older age; however, overall tumor genetics provided limited information to predict individual patient risk. Our approach identifies 3 molecular subclusters of FL linked to differences in underlying mechanistic pathways. These clusters, which may be further resolved by the inclusion of translocation status and wider mutation profiles, have implications for understanding pathogenesis as well as improving treatment strategies in the future.

Genomic and microenvironmental landscape of stage I follicular lymphoma, compared with stage III/IV

Although the genomic and immune microenvironmental landscape of follicular lymphoma (FL) has been extensively investigated, little is known about the potential biological differences between stage I and stage III/IV disease. Using next-generation sequencing and immunohistochemistry, 82 FL nodal stage I cases were analyzed and compared with 139 FL stage III/IV nodal cases. Many similarities in mutations, chromosomal copy number aberrations, and microenvironmental cell populations were detected. However, there were also significant differences in microenvironmental and genomic features. CD8+ T cells (P = .02) and STAT6 mutations (false discovery rate [FDR] <0.001) were more frequent in stage I FL. In contrast, programmed cell death protein 1-positive T cells, CD68+/CD163+ macrophages (P < .001), BCL2 translocation (BCL2trl+) (P < .0001), and KMT2D (FDR = 0.003) and CREBBP (FDR = 0.04) mutations were found more frequently in stage III/IV FL. Using clustering, we identified 3 clusters within stage I, and 2 clusters within stage III/IV. The BLC2trl+ stage I cluster was comparable to the BCL2trl+ cluster in stage III/IV. The two BCL2trl- stage I clusters were unique for stage I. One was enriched for CREBBP (95%) and STAT6 (64%) mutations, without BLC6 translocation (BCL6trl), whereas the BCL2trl- stage III/IV cluster contained BCL6trl (64%) with fewer CREBBP (45%) and STAT6 (9%) mutations. The other BCL2trl- stage I cluster was relatively heterogeneous with more copy number aberrations and linker histone mutations. This exploratory study shows that stage I FL is genetically heterogeneous with different underlying oncogenic pathways. Stage I FL BCL2trl- is likely STAT6 driven, whereas BCL2trl- stage III/IV appears to be more BCL6trl driven.

The International Consensus Classification of Mature Lymphoid Neoplasms: a report from the Clinical Advisory Committee

Since the publication of the Revised European-American Classification of Lymphoid Neoplasms in 1994, subsequent updates of the classification of lymphoid neoplasms have been generated through iterative international efforts to achieve broad consensus among hematopathologists, geneticists, molecular scientists, and clinicians. Significant progress has recently been made in the characterization of malignancies of the immune system, with many new insights provided by genomic studies. They have led to this proposal. We have followed the same process that was successfully used for the third and fourth editions of the World Health Organization Classification of Hematologic Neoplasms. The definition, recommended studies, and criteria for the diagnosis of many entities have been extensively refined. Some categories considered provisional have now been upgraded to definite entities. Terminology for some diseases has been revised to adapt nomenclature to the current knowledge of their biology, but these modifications have been restricted to well-justified situations. Major findings from recent genomic studies have impacted the conceptual framework and diagnostic criteria for many disease entities. These changes will have an impact on optimal clinical management. The conclusions of this work are summarized in this report as the proposed International Consensus Classification of mature lymphoid, histiocytic, and dendritic cell tumors.

The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Lymphoid Neoplasms

We herein present an overview of the upcoming 5^th edition of the World Health Organization Classification of Haematolymphoid Tumours focussing on lymphoid neoplasms. Myeloid and histiocytic neoplasms will be presented in a separate accompanying article. Besides listing the entities of the classification, we highlight and explain changes from the revised 4^th edition. These include reorganization of entities by a hierarchical system as is adopted throughout the 5^th edition of the WHO classification of tumours of all organ systems, modification of nomenclature for some entities, revision of diagnostic criteria or subtypes, deletion of certain entities, and introduction of new entities, as well as inclusion of tumour-like lesions, mesenchymal lesions specific to lymph node and spleen, and germline predisposition syndromes associated with the lymphoid neoplasms.

Necrotizing Follicular Lymphoma of the Inguinal Region with Sternbergoid Cells: Clinical–Pathological Features of a Challenging Entity

Follicular lymphoma (FL) is one of the most common B-cell malignancies worldwide. While the diagnosis of conventional cases is straightforward, rare clinical–pathological variants may be challenging due to their misleading morphology, aberrant phenotype and/or atypical presentation. To add to the spectrum of unusual FLs, we report on a rare disease pattern characterized by (i) inguinal presentation, (ii) massive necrosis, (iii) Hodgkin/Reed–Sternberg (HRS)-like cells, and (iv) adjacent areas of diffuse large B-cell lymphoma evolution. All cases occurred in elderly patients (median age at diagnosis: 69.5 years), disclosed a low stage at diagnosis (Ann Arbor stage IA-IIA), and had deceiving clinical features. Despite the alarming histology, excellent responses to conventional therapies were reported in all patients. In conclusion, necrotizing FL of the inguinal region is a rare neoplasm characterized by peculiar clinical and histological features. This lymphoma should always be considered in the differential diagnosis of massively necrotic inguinal lesions.

Follicular lymphoma: updates for pathologists

Follicular lymphoma (FL) is the most common indolent B-cell lymphoma and originates from germinal center B-cells (centrocytes and centroblasts) of the lymphoid follicle. Tumorigenesis is believed to initiate early in precursor B-cells in the bone marrow (BM) that acquire the t(14;18)(q32;q21). These cells later migrate to lymph nodes to continue their maturation through the germinal center reaction, at which time they acquire additional genetic and epigeneticabnormalities that promote lymphomagenesis. FLs are heterogeneous in terms of their clinicopathologic features. Most FLs are indolent and clinically characterized by peripheral lymphadenopathy with involvement of the spleen, BM, and peripheral blood in a substantial subset of patients, sometimes accompanied by constitutional symptoms and laboratory abnormalities. Diagnosis is established by the histopathologic identification of a B-cell proliferation usually distributed in an at least partially follicular pattern, typically, but not always, in a lymph node biopsy. The B-cell proliferation is biologically of germinal center cell origin, thus shows an expression of germinal center-associated antigens as detected by immunophenotyping. Although many cases of FLs are typical and histopathologic features are straightforward, the biologic and histopathologic variability of FL is wide, and an accurate diagnosis of FL over this disease spectrum requires knowledge of morphologic variants that can mimic other lymphomas, and rarely non-hematologic malignancies, clinically unique variants, and pitfalls in the interpretation of ancillary studies. The overall survival for most patients is prolonged, but relapses are frequent. The treatment landscape in FL now includes the application of immunotherapy and targeted therapy in addition to chemotherapy.

STAT6 and phosphorylated STAT6 are differentially expressed in lymphomas

BACKGROUND

The STAT6 pathway is implicated in the pathogenesis of various lymphomas; however, its immunohistochemical expression has not been fully investigated. Thus, the aim of this study was to investigate the immunohistochemical expression of the two forms of STAT6, phosphorylated or not, in a series of systemic lymphomas.

MATERIALS AND METHODS

Immunohistochemical expression of two antibodies, STAT6 (clone YE361) and pSTAT6 (clone Y641), which recognise the phosphorylated form of the molecule was studied in 60 lymphomas.

RESULTS

STAT6^YE361 expression was cytoplasmic, with 23.3% of the cases showing high expression. pSTAT6^Y641 expression was mostly nuclear and found in 45% of the cases. pSTAT6^Y641 nuclear expression was associated with the lymphoma type (p < 0.0001), as it was seen mostly in follicular, Hodgkin and angioimmunoblastic T cell lymphomas. STAT6^YE361 cytoplasmic expression was also associated with lymphoma type (p = 0.001), as it was mostly found in diffuse large B cell and marginal B cell lymphomas. No association with PD-L1 expression, other clinicopathological data or prognosis was found.

CONCLUSION

The two STAT6 clones are differentially expressed between lymphoma types.

Expression of STAT6 and Phosphorylated STAT6 in Primary Central Nervous System Lymphomas

The signal transducer and activator of transcription 6 (STAT6) is implicated in the pathogenesis of some lymphomas including primary central nervous system lymphomas (PCNSLs). The aim of this study was to investigate STAT6 expression and clinicopathologic features in 25 PCNSLs using immunohistochemistry with 2 different anti-STAT6 antibodies. One (YE361) recognizes the C-terminus domain of the STAT6 protein and the other (Y641) recognizes the phosphorylated form of the protein. The phosphorylated STAT6 form was not expressed in any of the cases studied whereas the YE361 STAT6 showed only cytoplasmic expression in 14 (56%) cases. This expression did not correlate with age, prognostic score, multiplicity, invasion of deep structures, response to treatment, disease recurrence, overall survival, or BCL6, BCL2, PD-L1, and CD8 expression. A STAT6 expression score showed a trend for correlating with clinical performance status. It also showed a positive correlation with MYC expression. Thus, the phosphorylated form of STAT6 was not found in the current series, while the YE361 STAT6 showed only cytoplasmic expression and was associated with expression of MYC.

Follicular lymphoma t(14;18)-negative is genetically a heterogeneous disease

Fifty-five cases of t(14;18)- follicular lymphoma (FL) were genetically characterized by targeted sequencing and copy number (CN) arrays. t(14;18)- FL predominated in women (M/F 1:2); patients often presented during early clinical stages (71%), and had excellent prognoses. Overall, t(14;18)- FL displayed CN alterations (CNAs) and gene mutations carried by conventional t(14;18)+ FL (cFL), but with different frequencies. The most frequently mutated gene was STAT6 (57%) followed by CREBBP (49%), TNFRSF14 (39%), and KMT2D (27%). t(14;18)- FL showed significantly more STAT6 mutations and lacked MYD88, NOTCH2, MEF2B, and MAP2K1 mutations compared with cFL, nodal marginal zone lymphoma (NMZL), and pediatric-type FL (PTFL). We identified 2 molecular clusters. Cluster A was characterized by TNFRSF14 mutations/1p36 alterations (96%) and frequent mutations in epigenetic regulators, with recurrent loss of 6q21-24 sharing many features with cFL. Cluster B showed few genetic alterations; however, a subgroup with STAT6 mutations concurrent with CREBBP mutations/16p alterations without TNFRSF14 and EZH2 mutations was noted (65%). These 2 molecular clusters did not distinguish cases by inguinal localization, growth pattern, or presence of STAT6 mutations. BCL6 rearrangements were demonstrated in 10 of 45 (22%) cases and did not cluster together. Cases with predominantly inguinal presentation (20 of 50; 40%) had a higher frequency of diffuse growth pattern, STAT6 mutations, CD23 expression, and a lower number of CNAs, in comparison with noninguinal cases (5.1 vs 9.1 alterations per case; P < .05). STAT6 mutations showed a positive correlation with CD23 expression (P < .001). In summary, t(14;18)- FL is genetically a heterogeneous disorder with features that differ from cFL, NMZL, and PTFL.

STAT6: A review of a signaling pathway implicated in various diseases with a special emphasis in its usefulness in pathology

Signal Transducer and Activator of Transcription 6 (STAT6), belonging to a family of seven similar members is primarily stimulated by interleukin(IL)-4 and IL-13, and acts as a T helper type 2 (Th2)-inducing factor. Thus, it is implicated in the pathophysiology of various allergic conditions, such as asthma, atopic dermatitis, eosinophilic esophagitis and food allergies, but also in tumor microenvironment regulation. Furthermore, certain forms of lymphomas, notably the Hodgkin lymphoma group, the primary mediastinal and primary central nervous system lymphoma, as well as some follicular and T cell lymphomas are associated with dysregulation of the STAT6 pathway. STAT6 immunohistochemical expression also serves as a surrogate marker in the diagnosis of solitary fibrous tumor, despite not directly responsible for the tumorigenic effect. These pathophysiological implications of the STAT6 pathway, its diagnostic or prognostic role in pathology, as well its immunohistochemical detection with different antibodies will be discussed in this review.

New developments in non-Hodgkin lymphoid malignancies

The revised fourth edition of the World Health Organization (WHO) Classification of Tumours of Haematopoietic and Lymphoid Tissues (2017) reflects significant advances in understanding the biology, genetic basis and behaviour of haematopoietic neoplasms. This review focuses on some of the major changes in B-cell and T-cell non-Hodgkin lymphomas in the 2017 WHO and includes more recent updates. The 2017 WHO saw a shift towards conservatism in the classification of precursor lesions of small B-cell lymphomas such as monoclonal B-cell lymphocytosis, in situ follicular and in situ mantle cell neoplasms. With more widespread use of next generation sequencing (NGS), special entities within follicular lymphoma and mantle cell lymphoma were recognised with recurrent genetic aberrations and unique clinicopathological features. The diagnostic workup of lymphoplasmacytic lymphoma and hairy cell leukaemia has been refined with the discovery of MYD88 L265P and BRAF V600E mutations, respectively, in these entities. Recommendations in the immunohistochemical evaluation of diffuse large B-cell lymphoma include determining cell of origin and expression of MYC and BCL2, so called 'double-expressor' phenotype. EBV-positive large B-cell lymphoma of the elderly has been renamed to recognise its occurrence amongst a wider age group. EBV-positive mucocutaneous ulcer is a newly recognised entity with indolent clinical behaviour that occurs in the setting of immunosuppression. Two lymphomas with recurrent genetic aberrations are newly included provisional entities: Burkitt-like lymphoma with 11q aberration and large B-cell lymphoma with IRF4 rearrangement. Aggressive B-cell lymphomas with MYC, BCL2 and/or BCL6 rearrangements, so called 'double-hit/triple-hit' lymphomas are now a distinct entity. Much progress has been made in understanding intestinal T-cell lymphomas. Enteropathy-associated T-cell lymphoma, type II, is now known to not be associated with coeliac disease and is hence renamed monomorphic epitheliotropic T-cell lymphoma. An indolent clonal T-cell lymphoproliferative disorder of the GI tract is a newly included provisional entity. Angioimmunoblastic T-cell lymphoma and nodal T-cell lymphomas with T-follicular helper phenotype are included in a single broad category, emphasising their shared genetic and phenotypic features. Anaplastic large cell lymphoma, ALK- is upgraded to a definitive entity with subsets carrying recurrent rearrangements in DUSP22 or TP63. Breast implant-associated anaplastic large cell lymphoma is a new provisional entity with indolent behaviour. Finally, cutaneous T-cell proliferations include a new provisional entity, primary cutaneous acral CD8-positive T-cell lymphoma, and reclassification of primary small/medium CD4-positive T-cell lymphoma as lymphoproliferative disorder.

The roles of post-translational modifications and coactivators of STAT6 signaling in tumor growth and progression

Signal transducers and activators of transcription 6 (STAT6) are highly expressed in various tumors and associated with tumorigenesis, immunosuppression, proliferation, metastasis and poor prognosis in human cancers. In response to IL-4/13, STAT6 is phosphorylated, dimerizes and triggers transcriptional regulation after recruitment of coactivators to transcriptosome, such as CBP/p300, SRC-1, PARP-14 and PSF. Post-translational modifications, including phosphorylation, ubiquitination, ADP-ribosylation and acetylation, have been explored for molecular mechanisms of STAT6 in tumor development and management. STAT6 has been developed as a specific biomarker for distinguishing and diagnosing tumor phenotypes, although it is observed to be frequently mutated in metastatic tumors. In this article, we focus mainly on the structural characteristics of STAT6 and its role in tumor growth and progression.

The molecular landscape and other distinctive features of primary cutaneous follicle center lymphoma

Primary cutaneous follicle center lymphoma (PCFCL) is distinguished from other follicular lymphomas (FLs) based on its clinicopathologic features including diminished CD10 and frequent lack of BCL2 rearrangements (R). Whether newer germinal center-associated markers would also be less commonly expressed and whether mutational studies would support its segregation from classic FL and FL subsets, including those which also typically lack BCL2R, are uncertain. To address these questions, 22 PCFCLs were stained for myocyte enhancer factor 2B (MEF2B) and human germinal center-associated lymphoma (HGAL), and targeted next-generation sequencing was performed with results compared to a meta-analysis of FL, pediatric-type FL (PTFL), low stage FL (LSFL) and other FL subsets. Selected fluorescence in situ hybridization studies were also performed. Although 27% of cases lacked CD10, all tested were MEF2B+ and HGAL+. The most common somatic mutations in the 12 to 19 analyzable PCFCL were TNFRSF14 (40%, plus 10% with 1p36 deletions), followed by CREBBP, TNFAIP3, KMT2D, SOCS1, EP300, STAT6, and FOXO1 (17-25%). Three of the most commonly mutated genes in FL (KMT2D, CREBBP, and BCL2) were significantly less commonly mutated in PCFCL than in FL, and TNFAIP was more commonly mutated with no difference for TNFRSF14 between PCFCL and FL or PTFL. CREBBP was also less frequently mutated than in LSFL but more frequently mutated than in PTFL. MAP2K1 mutations were much more common in PTFL (44% versus 0%). Two of 22 of the PCFCL had a BCL2 rearrangement and zero of 12 had a BCL6 rearrangement. These findings, while showing well-recognized and new shared features between PCFCL and other FL, highlight a distinctive mutational profile further supporting its recognition as a distinct entity.

CREBBP and STAT6 co-mutation and 16p13 and 1p36 loss define the t(14;18)-negative diffuse variant of follicular lymphoma

The diffuse variant of follicular lymphoma (dFL) is a rare variant of FL lacking t(14;18) that was first described in 2009. In this study, we use a comprehensive approach to define unifying pathologic and genetic features through gold-standard pathologic review, FISH, SNP-microarray, and next-generation sequencing of 16 cases of dFL. We found unique morphologic features, including interstitial sclerosis, microfollicle formation, and rounded nuclear cytology, confirmed absence of t(14;18) and recurrent deletion of 1p36, and showed a novel association with deletion/CN-LOH of 16p13 (inclusive of CREBBP, CIITA, and SOCS1). Mutational profiling demonstrated near-uniform mutations in CREBBP and STAT6, with clonal dominance of CREBBP, among other mutations typical of germinal-center B-cell lymphomas. Frequent CREBBP and CIITA codeletion/mutation suggested a mechanism for immune evasion, while subclonal STAT6 activating mutations with concurrent SOCS1 loss suggested a mechanism of BCL-xL/BCL2L1 upregulation in the absence of BCL2 rearrangements. A review of the literature showed significant enrichment for 16p13 and 1p36 loss/CN-LOH, STAT6 mutation, and CREBBP and STAT6 comutation in dFL, as compared with conventional FL. With this comprehensive approach, our study demonstrates confirmatory and novel genetic associations that can aid in the diagnosis and subclassification of this rare type of lymphoma.

Diffuse follicular lymphoma variant with a typical diagnostic pattern and an unusually aggressive clinical presentation

Diffuse follicular lymphoma (FL) variant is a rare condition that shows distinctive clinical, morphological, immunophenotypic, and molecular features that distinguish it from classical FL. Diffuse FL variant is characterized by a predominantly diffuse growth pattern, absence of the t (14;18) IGH/BCL2 translocation, CD23 expression, and presence of 1p36 deletion. Gene mutations involving STAT6 have been reported, with nuclear expression of STAT6 and phosphorylated STAT6 detected by immunohistochemistry. Patients frequently present with inguinal node involvement and low clinical stage. We describe the case of an 80-year-old female diagnosed with diffuse FL variant, presented with a classic diagnostic pattern and an unusual aggressive clinical onset.

Diagnostic utility of STAT6YE361 expression in classical Hodgkin lymphoma and related entities

Although the distinction of classical Hodgkin lymphoma from nodular lymphocyte predominant Hodgkin lymphoma using morphology and immunostains is straightforward in most instances, occasional cases pose diagnostic challenge. We sought to determine the utility of the novel YE361 STAT6 rabbit monoclonal antibody in Hodgkin lymphoma and diagnostically challenging B- and T-cell non-Hodgkin lymphoma entities with Hodgkin-like features. Cases from seven institutions included: 57 classical Hodgkin lymphomas (31% EBV+), 34 nodular lymphocyte predominant Hodgkin lymphomas, 34 mimicking B- and T-cell non-Hodgkin lymphomas, and 7 reactive lymphoproliferations. After review of histology, STAT6^YE361 immunostaining was performed. The intensity and spatial localization of immunopositivity was assessed in neoplastic cells. Additional FISH for programmed death ligand-1 (PD-L1) was performed in one patient in paired treatment-naive and relapse biopsy tissues. Two STAT6^YE361 immunopositive cases were examined by whole-exome sequencing after flow sorting to assess mutations in STAT6 pathway genes. Most classical Hodgkin lymphomas showed nuclear staining for STAT6^YE361 [46/57 cases (80%)] on Hodgkin cells. Staining was exclusively nuclear in a minority [12/46 (26%)], while dual nuclear and cytoplasmic localization was more common [34/46 (74%)]. In contrast, all nodular lymphocyte predominant Hodgkin lymphomas [0/34 (0%)] were negative for nuclear STAT6^YE361 staining on the lymphocyte predominant cells. Within B- and T-cell non-Hodgkin lymphomas, nuclear STAT6^YE361 was seen in: B-cell lymphoma unclassifiable with features intermediate between diffuse large B-cell lymphoma and classical Hodgkin lymphoma, and in primary mediastinal large B-cell lymphoma. Strong PD-L1 gene amplification was noted in the paired cHL and relapse B-cell lymphoma unclassifiable with features intermediate between diffuse large B-cell lymphoma and classical Hodgkin lymphoma, although STAT6^YE361 was negative in both biopsies. Whole-exome sequencing identified mutations in B2M, XPO1, and ITPKB as well CISHP213L (in the STAT pathway) in one classical Hodgkin lymphoma patient positive for nuclear STAT6^YE361 although no underlying STAT6 mutations were observed in either sample examined. STAT6^YE361 nuclear staining has 100% positive predictive value and 85.7% negative predictive value in confirming or excluding classical Hodgkin lymphoma diagnosis in the distinction from nodular lymphocyte predominant Hodgkin lymphoma and other benign and malignant entities.

The broad landscape of follicular lymphoma: Part I

Follicular lymphoma is a neoplasm derived from follicle center B cells, typically both centrocytes and centroblasts, in variable proportions according to the lymphoma grading. The pattern of growth may be entirely follicular, follicular and diffuse, and rarely completely diffuse. It represents the second most common non-Hodgkin lymphoma, after diffuse large B-cell lymphoma and is the most common low-grade mature B-cell lymphoma in western countries. In the majority of cases, follicular lymphoma is a nodal tumor, occurring in adults and frequently associated with the translocation t(14;18)(q32;q21)/IGH-BCL2. However, in recent years the spectrum of follicular lymphoma has expanded and small subsets of follicular lymphoma, which differ from common follicular lymphoma, have been identified and included in the current 2017 WHO classification. The aim of our review is to describe the broad spectrum of follicular lymphoma, pointing out that the identification of distinct clinicopathological variants of follicular lymphoma is relevant for patient outcomes and choice of treatment.

Flow cytometry aneuploidy and cell cycle indexing as a possible tool for differentiating between CD10+ diffuse large B-cell lymphoma and follicular lymphoma

BACKGROUND

Differential diagnosis between diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) becomes a challenge when adequate biopsy is unavailable. The present study aimed to investigate the applicability of DNA cell cycle analysis by flow cytometry (FC) for differentiating between CD10⁺ DLBCL and FL.

METHODS

Data were collected from 57 specimens where CD5^- /CD10⁺ /light chain restricted B cells were detected. DNA staining was performed using the Coulter DNA Prep Kit. Cell cycle fractions were evaluated by automatic analysis using the ModFit LT software.

RESULTS

Histopathological analysis confirmed the diagnosis of CD10⁺ FL in 30 specimens (52.6%), CD10⁺ DLBCL in 24 specimens (42.1%), and CD10⁺ Burkitt lymphoma in 3 specimens (5.3%). A significantly higher rate of DNA aneuploidy was detected among CD10⁺ DLBCL than FL specimens (50 vs. 13.3% respectively, p = .003). Likewise, DNA index was significantly higher in CD10⁺ DLBCL relative to FL (1.26 ± 0.35 vs. 1.04 ± 0.16 respectively, p = .004). Notably, the proportion of cells in the S-phase and proliferative fraction was significantly higher in CD10⁺ DLBCL than in CD10⁺ FL (S-phase: 15.97 ± 13.94 vs. 4.43 ± 4.41 mean ± SD, respectively, p < .0001; proliferative fraction: 18.87 ± 15.17 vs. 5.78 ± 7.04 mean ± SD, respectively, p = .0001). Using a receiver operating characteristic analysis, optimal cutoffs for S-phase ≥7% and proliferative fraction ≥9% were determined. These values could be used to differentiate between CD10⁺ DLBCL and CD10⁺ FL.

CONCLUSION

Including DNA cell cycle analysis in the FC lymphoma assessment panel may be of diagnostic value in differentiating between CD10+ DLBCL and FL when adequate biopsy is unavailable.

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.

Diagnostically relevant updates to the 2017 WHO classification of lymphoid neoplasms

The recent 2017 WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues contains a number of updates under the category of lymphoid neoplasms. These changes include introduction of new entities, amended classification or terminology, and addition of newly discovered diagnostic and molecular features. In this review, we perform a focused, concise summary of selected lymphoid neoplasms and discuss changes in their classification. Rather than a comprehensive overview, we place specific emphasis on important and diagnostically relevant aspects of each entity that are novel or different from the previous WHO iteration and bring the practicing pathologist quickly up to speed with the updated classification.

Follicular Lymphoma Diagnostic Caveats and Updates

CONTEXT.—

Follicular lymphoma is a common small B-cell lymphoma, likely to be encountered by any practicing pathologist, regardless of specialty. Although the features of typical follicular lymphoma are well known and in most instances easily identifiable, there are lesser-appreciated morphologic appearances that can raise alternative diagnostic possibilities. The limited tissue available in core needle biopsies can make it additionally challenging to thoroughly evaluate those features in the context of architecture. Furthermore, ancillary testing including immunohistochemistry and molecular/genetic analysis do not always show classic findings and may pose additional challenges to interpretation.

OBJECTIVES.—

To review the morphologic features of follicular lymphoma with a discussion of morphologic variants and mimics; to discuss pitfalls of ancillary testing and provide the practicing pathologist with an appropriate context for interpretation of immunohistochemical and molecular/genetic studies when follicular lymphoma is part of the differential diagnosis; and to propose diagnostic strategies when there is limited tissue for evaluation.

DATA SOURCES.—

We used examples of follicular lymphoma from our institution as well as a review of the literature, with a focus on the diagnostic aspects that are broadly relevant to a general pathology practice.

CONCLUSIONS.—

Follicular lymphoma can occasionally present with atypical morphologic, immunohistochemical, or molecular/genetic features. In particular, those findings can be difficult to interpret in the setting of a limited tissue sample. Awareness of those possibilities will help guide the pathologist to a more accurate and precise diagnosis.

Reduced lymphotoxin-beta production by tumour cells is associated with loss of follicular dendritic cell phenotype and diffuse growth in follicular lymphoma

Cytokine production is essential for follicular dendritic cell (FDC) maintenance and organization of germinal centres. In follicular lymphoma, FDCs are often disarrayed and may lack antigens indicative of terminal differentiation. We investigated the in situ distribution of cells producing lymphotoxin‐beta (LTB), lymphotoxin‐alpha (LTA), and tumour necrosis factor‐alpha (TNFA) transcripts in human reactive lymph nodes and in follicular lymphomas with follicular or diffuse growth pattern. LTB was the cytokine most abundantly produced in germinal centres. LTB was present in nearly 90% of germinal centre cells whereas LTA and TNFA were detected in 30 and 50%, respectively. Moreover, the amount of LTB expressed in reactive germinal centre cells was 80‐fold higher than that of LTA and 20‐fold higher than that of TNFA. LTB‐positive cells were more numerous in the germinal centre dark zone, whereas expression of the FDC proteins CD21, CD23, VCAM, and CXCL13 was more intense in the light zone. Tumour cells of follicular lymphomas produced less LTB than reactive germinal centre cells. The results of the in situ study were confirmed by RT‐PCR; LTB was significantly more abundant in reactive lymph nodes than in follicular lymphoma, with the lowest values detected in predominantly diffuse follicular lymphoma. In neoplastic follicles, low production of LTB by tumour B cells was associated with weaker expression of CD21+/CD23+ by FDCs. Our findings detail for the first time the distribution of LTA‐, LTB‐, and TNFA‐producing cells in human reactive germinal centres and in follicular lymphoma. They suggest the possibility that impaired tumour‐cell LTB production may represent a determinant of FDC phenotype loss and for defective follicular organization in follicular lymphoma.

The Pathology of Hyperthyroidism

This article reviews those pathologic lesions which are associated with clinical and/or biochemical hyperthyroidism. Beginning with the descriptive pathology of classical Graves' disease and the less common toxic nodular goiter and hyper-functioning thyroid nodules, this paper describes the effects of non-thyroidal hormones, glandular function (including pituitary and hypothalamic lesions), ectopic production of thyroid stimulating proteins by non-thyroidal neoplasms, exogenous drug reactions causing hyper-function and finally conditions associated with a mechanic- destructive cause of hyperthyroidism.

The exomic landscape of t(14;18)-negative diffuse follicular lymphoma with 1p36 deletion

Predominantly diffuse t(14;18) negative follicular lymphoma (FL) with 1p36 deletion shows distinctive clinical, morphological and molecular features that distinguish it from classical FL. In order to investigate whether it possesses a unique mutation profile, we performed whole exome sequencing of six well-characterised cases. Our analysis showed that the mutational landscape of this subtype is largely distinct from classical FL. It appears to harbour several recurrent mutations, affecting STAT6, CREBBP and basal membrane protein genes with high frequency. Our data support the view that this FL subtype should be considered a separate entity from classical FL.

Clinical utility of recently identified diagnostic, prognostic, and predictive molecular biomarkers in mature B-cell neoplasms

Genomic profiling studies have provided new insights into the pathogenesis of mature B-cell neoplasms and have identified markers with prognostic impact. Recurrent mutations in tumor-suppressor genes (TP53, BIRC3, ATM), and common signaling pathways, such as the B-cell receptor (CD79A, CD79B, CARD11, TCF3, ID3), Toll-like receptor (MYD88), NOTCH (NOTCH1/2), nuclear factor-κB, and mitogen activated kinase signaling, have been identified in B-cell neoplasms. Chronic lymphocytic leukemia/small lymphocytic lymphoma, diffuse large B-cell lymphoma, follicular lymphoma, mantle cell lymphoma, Burkitt lymphoma, Waldenström macroglobulinemia, hairy cell leukemia, and marginal zone lymphomas of splenic, nodal, and extranodal types represent examples of B-cell neoplasms in which novel molecular biomarkers have been discovered in recent years. In addition, ongoing retrospective correlative and prospective outcome studies have resulted in an enhanced understanding of the clinical utility of novel biomarkers. This progress is reflected in the 2016 update of the World Health Organization classification of lymphoid neoplasms, which lists as many as 41 mature B-cell neoplasms (including provisional categories). Consequently, molecular genetic studies are increasingly being applied for the clinical workup of many of these neoplasms. In this review, we focus on the diagnostic, prognostic, and/or therapeutic utility of molecular biomarkers in mature B-cell neoplasms.

Diagnostic value of STMN1, LMO2, HGAL, AID expression and 1p36 chromosomal abnormalities in primary cutaneous B cell lymphomas

AIMS

Distinction between primary cutaneous follicular lymphoma (PCFL) and primary cutaneous marginal zone lymphoma (PCMZL) is challenging, as clear-cut immunophenotypical and cytogenetic criteria to segregate both entities are lacking.

METHODS AND RESULTS

To characterize PCFL and PCMZL more clearly and to define criteria helpful for the differential diagnosis, we compared expression of immunohistochemical markers [LIM-only transcription factor 2 (LMO2), human germinal centre-associated lymphoma (HGAL), stathmin 1 (STMN1), activation-induced cytidine deaminase (AID), myeloid cell nuclear differentiation antigen (MNDA)] and the presence of cytogenetic abnormalities described previously in nodal follicular lymphoma [B cell lymphoma 2 (BCL2) and BCL6 breaks, 1p36 chromosomal region deletion (del 1p36)] in a series of 48 cutaneous follicular and marginal zone lymphomas [cutaneous follicular lymphoma (CFL) and cutaneous marginal zone lymphoma (CMZL)]. Immunostaining for STMN1, LMO2, HGAL and AID allowed the distinction between CFL and CMZL, and STMN1 was the most sensitive marker (100% CFL, 0% CMZL). LMO2, HGAL and AID were positive in 93.2%, 82.1% and 86.2% CFL (all CMZL-negative). MNDA was expressed in both entities without significant difference (10.3% CFL, 30.8% CMZL, P = 0.18). BCL2, BCL6 breaks and the del 1p36 were present in 16.7%, 10.7% and 18.5% CFL and no CMZL. Finally, three and 29 CFL were reclassified as secondary cutaneous follicular lymphomas (SCFL) and PCFL without significant differences concerning phenotypical and cytogenetic features. BCL2, BCL6 breaks and the del 1p36 were present in 11.1%, 8% and 16.7% PCFL and did not impact the prognosis.

CONCLUSION

LMO2, HGAL, STMN1 and AID, but not MNDA, are discriminant for the recognition between CFL and CMZL. BCL2, BCL6 rearrangements and the del 1p36 have a role in the pathogenesis of PCFL, the latest being the most common alteration.

Diagnosis and classification of hematologic malignancies on the basis of genetics

Genomic analysis has greatly influenced the diagnosis and clinical management of patients affected by diverse forms of hematologic malignancies. Here, we review how genetic alterations define subclasses of patients with acute leukemias, myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPNs), non-Hodgkin lymphomas, and classical Hodgkin lymphoma. These include new subtypes of acute myeloid leukemia defined by mutations in RUNX1 or BCR-ABL1 translocations as well as a constellation of somatic structural DNA alterations in acute lymphoblastic leukemia. Among patients with MDS, detection of mutations in SF3B1 define a subgroup of patients with the ring sideroblast form of MDS and a favorable prognosis. For patients with MPNs, detection of the BCR-ABL1 fusion delineates chronic myeloid leukemia from classic BCR-ABL1^- MPNs, which are largely defined by mutations in JAK2, CALR, or MPL In the B-cell lymphomas, detection of characteristic rearrangements involving MYC in Burkitt lymphoma, BCL2 in follicular lymphoma, and MYC/BCL2/BCL6 in high-grade B-cell lymphomas are essential for diagnosis. In T-cell lymphomas, anaplastic large-cell lymphoma is defined by mutually exclusive rearrangements of ALK, DUSP22/IRF4, and TP63 Genetic alterations affecting TP53 and the mutational status of the immunoglobulin heavy-chain variable region are important in clinical management of chronic lymphocytic leukemia. Additionally, detection of BRAFV600E mutations is helpful in the diagnosis of classical hairy cell leukemia and a number of histiocytic neoplasms. Numerous additional examples provided here demonstrate how clinical evaluation of genomic alterations have refined classification of myeloid neoplasms and major forms of lymphomas arising from B, T, or natural killer cells.