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.

Fifth Edition of the World Health Classification of Tumors of the Hematopoietic and Lymphoid Tissues: B-cell Neoplasms.

We review B-cell neoplasms in the 5th edition of the World Health Organization classification of hematolymphoid tumors (WHO-HEM5). The revised classification is based on a multidisciplinary approach including input from pathologists, clinicians, and other experts. The WHO-HEM5 follows a hierarchical structure allowing the use of family (class)-level definitions when defining diagnostic criteria are partially met or a complete investigational workup is not possible. Disease types and subtypes have expanded compared with the WHO revised 4th edition (WHO-HEM4R), mainly because of the expansion in genomic knowledge of these diseases. In this review, we focus on highlighting changes and updates in the classification of B-cell lymphomas, providing a comparison with WHO-HEM4R, and offering guidance on how the new classification can be applied to the diagnosis of B-cell lymphomas in routine practice.

Fifth Edition of the World Health Classification of Tumors of the Hematopoietic and Lymphoid Tissue: Myeloid Neoplasms.

In this manuscript, we review myeloid neoplasms in the fifth edition of the World Health Organization classification of hematolymphoid tumors (WHO-HEM5), focusing on changes from the revised fourth edition (WHO-HEM4R). Disease types and subtypes have expanded compared with WHO-HEM4R, mainly because of the expansion in genomic knowledge of these diseases. The revised classification is based on a multidisciplinary approach including input from a large body of pathologists, clinicians, and geneticists. The revised classification follows a hierarchical structure allowing usage of family (class)-level definitions where the defining diagnostic criteria are partially met or a complete investigational workup has not been possible. Overall, the WHO-HEM5 revisions to the classification of myeloid neoplasms include major updates and revisions with increased emphasis on genetic and molecular drivers of disease. The most notable changes have been applied to the sections of acute myeloid leukemia and myelodysplastic neoplasms (previously referred to as myelodysplastic syndrome) with incorporation of novel, disease-defining genetic changes. In this review we focus on highlighting the updates in the classification of myeloid neoplasms, providing a comparison with WHO-HEM4R, and offering guidance on how the new classification can be applied to the diagnosis of myeloid neoplasms in routine practice.

Fifth Edition of the World Health Organization Classification of Tumors of the Hematopoietic and Lymphoid Tissues: Acute Lymphoblastic Leukemias, Mixed-Phenotype Acute Leukemias, Myeloid/Lymphoid Neoplasms With Eosinophilia, Dendritic/Histiocytic Neoplasms, and Genetic Tumor Syndromes.

This manuscript represents a review of lymphoblastic leukemia/lymphoma (acute lymphoblastic leukemia/lymphoblastic lymphoma), acute leukemias of ambiguous lineage, mixed-phenotype acute leukemias, myeloid/lymphoid neoplasms with eosinophilia and defining gene rearrangements, histiocytic and dendritic neoplasms, and genetic tumor syndromes of the 5th edition of the World Health Organization Classification of Tumors of the Hematopoietic and Lymphoid Tissues. The diagnostic, clinicopathologic, cytogenetic, and molecular genetic features are discussed. The differences in comparison to the 4th revised edition of the World Health Organization classification of hematolymphoid neoplasms are highlighted.

Fifth Edition of the World Health Organization Classification of Tumors of the Hematopoietic and Lymphoid Tissues: Mature T-Cell, NK-Cell, and Stroma-Derived Neoplasms of Lymphoid Tissues.

This review focuses on mature T cells, natural killer (NK) cells, and stroma-derived neoplasms in the fifth edition of the World Health Organization classification of hematolymphoid tumors, including changes from the revised fourth edition. Overall, information has expanded, primarily due to advancements in genomic understanding. The updated classification adopts a hierarchical format. The updated classification relies on a multidisciplinary approach, incorporating insights from a diverse group of pathologists, clinicians, and geneticists. Indolent NK-cell lymphoproliferative disorder of the gastrointestinal tract, Epstein-Barr virus-positive nodal T- and NK-cell lymphoma, and several stroma-derived neoplasms of lymphoid tissues have been newly introduced or included. The review also provides guidance on how the fifth edition of the World Health Organization classification of hematolymphoid tumors can be applied in routine clinical practice.

Systems medicine dissection of chr1q-amp reveals a novel PBX1-FOXM1 axis for targeted therapy in multiple myeloma.

Understanding the biological and clinical impact of copy number aberrations (CNAs) on the development of precision therapies in cancer remains an unmet challenge. Genetic amplification of chromosome 1q (chr1q-amp) is a major CNA conferring an adverse prognosis in several types of cancer, including in the blood cancer multiple myeloma (MM). Although several genes across chromosome 1 (chr1q) portend high-risk MM disease, the underpinning molecular etiology remains elusive. Here, with reference to the 3-dimensional (3D) chromatin structure, we integrate multi-omics data sets from patients with MM with genetic variables to obtain an associated clinical risk map across chr1q and to identify 103 adverse prognosis genes in chr1q-amp MM. Prominent among these genes, the transcription factor PBX1 is ectopically expressed by genetic amplification and epigenetic activation of its own preserved 3D regulatory domain. By binding to reprogrammed superenhancers, PBX1 directly regulates critical oncogenic pathways and a FOXM1-dependent transcriptional program. Together, PBX1 and FOXM1 activate a proliferative gene signature that predicts adverse prognosis across multiple types of cancer. Notably, pharmacological disruption of the PBX1-FOXM1 axis with existing agents (thiostrepton) and a novel PBX1 small molecule inhibitor (T417) is selectively toxic against chr1q-amp myeloma and solid tumor cells. Overall, our systems medicine approach successfully identifies CNA-driven oncogenic circuitries, links them to clinical phenotypes, and proposes novel CNA-targeted therapy strategies in MM and other types of cancer.

Abnormal bone marrow findings in patients following treatment with chimeric antigen receptor-T cell therapy.

BACKGROUND: Bone marrow (BM) assessment after CAR-T cell immunotherapy infusion is not routinely performed to monitor adverse events such as cytopenias, hemophagocytic lymphohistiocytosis, or infections. Our institution has performed BM biopsies as part of CAR-T cell treatment protocols, encompassing pre- and post-treatment time points and during long-term follow-up. METHODS: We conducted a systematic retrospective review of BM abnormalities observed in samples from 259 patients following CAR-T cell immunotherapy. We correlated BM pathology findings with mortality, relapse/residual disease, and laboratory values. RESULTS: At a median of 35.5 days post-CAR-T infusion, 25.5% showed severe marrow hypocellularity, and 6.2% showed serous atrophy, and peripheral blood cytopenias corroborated these observations. Marrow features associated with reduced disease burden post-CAR-T infusion include increased lymphocytes seen in 16 patients and an increase of macrophages or granulomatous response seen in 25 patients. However, a 100-day landmark analysis also showed increased marrow histiocytes were associated with lower survival (median OS 6.0 vs. 21.4 months, p = .026), as was grade 2-3 marrow reticulin (18 patients) (median OS 12.5 vs. 24.2 months, p = .034). CONCLUSIONS: These data represent the first systematic observations of BM changes in patients receiving CAR-T cell immunotherapy.

Introduction to the Fifth Edition of the World Health Organization Classification of Tumors of Hematopoietic and Lymphoid Tissues.

The World Health Organization (WHO) Classification of Tumors of Hematopoietic and Lymphoid Tissues has been the internationally accepted standard for over 20 years. The fifth edition of the WHO Classification (WHO-HEM5) is a multidisciplinary effort by pathologists, clinicians and other specialists that builds upon the revised fourth edition published in 2017. Entities in WHO-HEM5 are organized hierarchically. There are several changes in WHO-HEM5 from the previous edition, including addition of new entities, deletion of some entities and recognition or revision of some subtypes reflecting scientific developments and clinical advances during the past few years. Essential and desirable criteria for each entity are included. Here we introduce WHO-HEM5. Four reviews will follow that emphasize important aspects of the classification.

The impact of histological grade on outcomes in follicular lymphoma: An analysis of patients in the SEER database in the context of evolving disease classification and treatment.

Currently, there is no convincing evidence that the grade of follicular lymphoma (FL) impacts patient outcome. We correlated grades in 33 925 patients with nodal FL during 1992-2018 in the SEER database with disease-specific survival (DSS) and overall survival (OS). Patients with FL grade 3 had lower DSS and OS as compared to FL grades 1-2. During 1992-2005, the 10-year DSS for patients with FL grades 3 and grades 1-2 were 68.6%, and 71.4%, respectively, and in 2006-2018, they were 77.7% and 82.6%, respectively. The 10-year OS estimates in 1992-2005 were 49.9% and 54.2% for grade 3 and grades 1-2 respectively, and in 2006-2018, they were 59.1% and 63.5% for grade 3 and grades 1-2, respectively. After adjustment for stage and age, the hazard ratios for death due to FL and death from any cause for patients with FL grade 3 during 1992-2005 were 1.09 (1.02-1.16) and 1.07 (1.02-1.12), respectively, compared to FL grades 1-2; and during 2006-2018, the hazard ratios for death due to FL and death from any cause for patients with FL grade 3 were 1.34 (1.22-1.45) and 1.16 (1.10-1.23), respectively compared to FL grades 1-2. The grade of FL is an important determinant of disease biology.

Parallel evolution of two distinct lymphoid proliferations in clonal haematopoiesis.

AIMS: Angioimmunoblastic T-cell lymphoma (AITL) is genetically characterized by TET2 and DNMT3A mutations occurring in haematopoietic progenitor cells, and late events (e.g. the RHOA-G17V mutation) associated with malignant transformation. As TET2/DNMT3A-mutated progenitor cells can differentiate into multilineage progenies and give rise to both AITL and myeloid neoplasms, they may also have the potential to lead to other metachronous/synchronous neoplasms. We report two cases showing parallel evolution of two distinct potentially neoplastic lymphoid proliferations from a common mutated haematopoietic progenitor cell population. METHODS AND RESULTS: Both cases presented with generalized lymphadenopathy. In case 1 (a 67-year-old female), an initial lymph node (LN) biopsy was dismissed as reactive, but a repeat biopsy showed a nodal marginal zone lymphoma (NMZL)-like proliferation with an increase in the number of T-follicular helper (TFH) cells. Immunohistochemistry, and clonality and mutational analyses by targeted sequencing of both whole tissue sections and microdissected NMZL-like lesions, demonstrated a clonal B-cell proliferation that harboured the BRAF-G469R mutation and shared TET2 and DNMT3A mutations with an underlying RHOA-G17V-mutant TFH proliferation. Review of the original LN biopsy showed histological and immunophenotypic features of AITL. In case 2 (a 66-year-old male), cytotoxic T-cell lymphoma with an increase in the number of Epstein-Barr virus-positive large B cells was diagnosed on initial biopsy. On review together with the relapsed biopsy, we identified an additional occult neoplastic TFH proliferation/smouldering AITL. Both T-cell proliferations shared TET2 and DNMT3A mutations while RHOA-G17V was confined to the smouldering AITL. CONCLUSIONS: In addition to demonstrating diagnostic challenges, these cases expand the potential of clonal haematopoiesis in the development of different lineage neoplastic proliferations.

CD5 + Gamma Delta T-Cell Lymphoproliferative Disorder/Lymphoma Without Cytotoxic Granules in the Skin.

ABSTRACT: We report a case of an unusual and aggressive gamma delta T-cell lymphoproliferative disorder/lymphoma presenting in the skin that lacked the expected cytotoxic markers and had increased expression of CD5, CD20, CD79a, CD30, and PD-1 without CD56. Monoclonal TCR-γ gene rearrangement was identified. A computed tomography scan of the chest, abdomen, and pelvis revealed a 7.7-cm soft-tissue inguinal mass and prominent retroperitoneal and pelvic lymphadenopathy, without hepatosplenomegaly. Flow cytometry finding on peripheral blood was normal. The clinical, morphologic, and immunophenotypic features of this case defy the current World Health Organization and European Organization for Research and Treatment of Cancer classifications, and a similar case has not been reported previously.

Indolent T-Cell Lymphoproliferative Disorder of the Uterine Corpus: A Case Report.

Primary lymphoproliferative disorders of the uterus are rare, with the majority being B-cell diseases or aggressive T-cell disease. We present the case of a 31-yr old in whom an Indolent T-cell lymphoproliferative disorder (iTCLPD) was identified in resection chippings for a suspected fibroid, following presentation with menorrhagia. Laboratory investigations revealed an oligoclonal T-cell infiltrate with the immunophenotype of nonactivated cytotoxic T cells, and a proliferative fraction of 10% to 15%. There was no clinical or radiologic evidence of systemic disease, and the patient remained well with no indication of relapse 1 yr from resection and diagnosis. iTCLPD of the uterine corpus has features in common with the recently described iTCLPD of the gastrointestinal tract and primary cutaneous acral CD8 T-cell lymphoma. Recognition of these parallels is important as few other cases of iTCLPD have been described, and it suggests local resection rather than systemic treatment as the best therapeutic strategy.

Mutational landscape of B-cell post-transplant lymphoproliferative disorders.

It is currently unclear whether post-transplant diffuse large B-cell lymphomas (PT-DLBCL) display a similar genomic landscape as DLBCL in immunocompetent patients (IC-DLBCL). We investigated 50 post-transplant lymphoproliferative disorders (PTLDs) including 37 PT-DLBCL samples for somatic mutations frequently observed in IC-DLBCL. Targeted Next Generation Sequencing (NGS) using the Ion Torrent platform and a customized panel of 68 genes was performed on genomic DNA. Non-tumoural tissue was sequenced to exclude germline variants in cases where available. A control cohort of 76 IC-DLBCL was available for comparative analyses. In comparison to IC-DLBCLs, PT-DLBCL showed more frequent mutations of TP53 (P = 0·004), and absence of ATM and B2M mutations (P = 0·004 and P = 0·016, respectively). In comparison to IC-DLBCLs, Epstein-Barr virus (EBV)+ PT-DLBCL had fewer mutated genes (P = 0·007) and particularly fewer mutations in nuclear factor-κB pathway-related genes (P = 0·044). TP53 mutations were more frequent in EBV- PT-DLBCL as compared to IC-DLBCL (P = 0·001). Germinal centre B cell (GCB) subtype of PT-DLBCL had fewer mutations and mutated genes than GCB-IC-DLBCLs (P = 0·048 and 0·04 respectively). Polymorphic PTLD displayed fewer mutations as compared to PT-DLBCL (P = 0·001). PT-DLBCL differs from IC-DLBCL with respect to mutations in genes related to DNA damage control and immune-surveillance, and EBV association is likely to have a bearing on the mutational pattern.

Bone marrow manifestations in multicentric Castleman disease.

This study aimed to document the morphological and immunophenotypic features, and describe the diagnostic features of bone marrow (BM) involvement in human herpes virus 8 Multicentric Castleman disease (HHV8-MCD). BM trephine biopsy (BMTB) specimens from 28 patients were revisited. Samples were evaluated for expression of CD3, CD20, CD138, CD68R, glycophorin C, CD42b, HHV8-latency-associated nuclear antigen (LANA1), Epstein-Barr virus-encoded small RNA and light chains. Presence of significant numbers of HHV8-LANA1(+) lymphoid/plasmacytic cells, noted in 10/28 cases, was indicative of BM involvement and was associated with low CD4 and CD8 counts in peripheral blood. The characteristic morphological appearance of MCD seen in lymph nodes is a rare finding in BMTB. 4/5 cases with lymphoid aggregates were involved by MCD, whereas 6/23 cases without lymphoid aggregates were involved by MCD (P = 0·023). 9/18 cases with hypercellular marrow were involved by MCD, whilst only 1/8 cases with normo/hypocellular marrow showed involvement by MCD (P = 0·070). While 9/21 cases with increased marrow reticulin were involved by MCD, none of the cases with no increase in reticulin were involved by MCD (P = 0·080). Reactive plasmacytosis is a frequent finding. We conclude that bone marrow is involved in a significant proportion of patients with MCD (36%), and involvement can be identified by HHV8-LANA1 immunohistochemistry.