High-grade B-cell lymphoma (HGBL)-NOS is clinicopathologically and genetically more similar to DLBCL/HGBL-DH than DLBCL

Diffuse Large B-Cell Lymphoma/High-Grade B-Cell Lymphoma With MYC and BCL6 Rearrangements: A Study of 60 Cases

Classification of cases of diffuse large B-cell lymphoma (DLBCL)/high-grade B-cell lymphoma (HGBL) with MYC and BCL6 rearrangements, referred to here as BCL6 double-hit lymphoma (DHL), is controversial. We assessed 60 cases of BCL6-DHL and compared this cohort to 224 cases of DHL with MYC and BCL2 rearrangements (BCL2-DHL) and 217 cases of DLBCL not otherwise specified. Compared with the DLBCL cohort, patients with BCL6-DHL had more aggressive clinical features such as frequent extranodal involvement, high-stage disease, a high International Prognostic Index score, and an elevated serum lactate dehydrogenase level (P < .01 for all). Compared with the BCL2-DHL cohort, patients with BCL6-DHL had similarly aggressive clinical features but a lower frequency of germinal center B-cell (GCB) immunophenotype and MYC and BCL2 double expression. Patients with BCL6-DHL showed overall survival (OS) intermediate between patients with DLBCL and BCL2-DHL. Following induction with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) chemotherapy, patients with BCL6-DHL demonstrated poor OS similar to patients with BCL2-DHL and worse OS than that of patients with DLBCL (P = .024). However, among patients who received rituximab, etoposide phosphate, prednisone, vincristine, cyclophosphamide, and doxorubicin (R-EPOCH), there was no significant difference in OS among the 3 groups (P = .146). Gene expression profiling showed that 60% of BCL6-DHL cases had a double-hit (DH)-like signature compared with 10% of DLBCL-GCB and 93% of BCL2-DHL cases. The DH-like signature in BCL6-DHL cases was associated with a GCB immunophenotype. Based on these data, we suggest that BCL6-DHL cases are clinically more aggressive than DLBCL and patients may benefit from a more aggressive therapy than R-CHOP. The data also suggest that BCL6-DHL, as currently defined, is heterogeneous and that neoplasms with a GCB immunophenotype are more likely to have a DH-like signature and behave more aggressively. Last, we suggest that BCL6-DHL cases deserve to be recognized separately in a lymphoma classification to facilitate further understanding of these neoplasms and for optimal patient management.

How I diagnose high-grade B-cell lymphoma

OBJECTIVES

High-grade B-cell lymphoma (HGBL), introduced in the 2016 World Health Organization (WHO) revised fourth edition classification, included cases defined by MYC and BCL2 and/or BCL6 rearrangements or by high-grade morphology. Diagnostic criteria and nomenclature for these lymphomas were refined in the 2022 WHO fifth edition (WHO-5) classification and International Consensus Classification (ICC). This review describes our approach to the diagnosis of HGBL.

METHODS

Two cases are presented illustrating how we diagnose HGBL, including 1 case harboring MYC and BCL6 rearrangements and a second showing TdT expression in an HGBL with MYC and BCL2 rearrangements. The ways in which these cases are distinguished from other lymphomas with high-grade features and the appropriate nomenclature using WHO-5 and ICC classifications are emphasized.

RESULTS

An HGBL diagnosis requires integration of morphology, immunophenotype, and genetics and exclusion of other lymphomas with high-grade morphology, including Burkitt lymphoma, B-lymphoblastic leukemia/lymphoma (B-LBL/ALL), and blastoid mantle cell lymphoma. A diagnosis of HGBL/large B-cell lymphoma with 11q aberration should also be considered in certain patient populations.

CONCLUSIONS

High-grade B-cell lymphomas are subclassified based on morphologic and genetic features. There are differences in the nomenclature and definition of these lymphomas in the WHO-5 and ICC classifications. Distinguishing HGBLs from other mature B-cell lymphomas and B-LBL/ALL is critical so that patients receive appropriate treatment.

A Diagnostic Approach in Large B-Cell Lymphomas According to the Fifth World Health Organization and International Consensus Classifications and a Practical Algorithm in Routine Practice

In this article, we provide a review of large B-cell lymphomas (LBCLs), comparing the recently published fifth edition of the WHO classification and the International Consensus Classification (ICC) on hematolymphoid tumors. We focus on updates in the classification of LBCL, an heterogeneous group of malignancies with varying clinical behaviors and different pathological and molecular features, providing a comparison between the two classifications. Besides the well-recognized diagnostic role of clinical, morphological and immunohistochemical data, both classifications recognize the ever-growing impact of molecular data in the diagnostic work-up of some entities. The main aim is to offer a guide for clinicians and pathologists on how the new classifications can be applied to LBCL diagnosis in routine practice. In the first part of the paper, we review the following categories: LBLs transformed from indolent B-cell lymphomas, diffuse large B-cell lymphoma, not otherwise specified (DLBCL, NOS), double-hit/triple-hit lymphomas (DH/TH), high-grade large B-cell lymphoma, not otherwise specified (HGBCL, NOS), LBCL with IRF4 rearrangement, Burkitt lymphoma (BL) and HGBCL/LBCL with 11q aberration, focusing on the differences between the two classifications. In the second part of the paper, we provide a practical diagnostic algorithm when facing LBCLs in routine daily practice.

Burkitt lymphoma

Burkitt lymphoma is a mature aggressive B-cell neoplasm with distinctive clinical and morphologic features, a germinal center B-cell immunophenotype, a high proliferation index and MYC rearrangement with an immunoglobulin gene partner. Initially described in equatorial Africa by a surgeon, Denis Burkitt, African (endemic) Burkitt lymphoma was the first neoplasm shown to be associated with a virus, Epstein-Barr virus (EBV), and the first neoplasm shown to be associated with a chromosomal translocation, IGH::MYC. In this article, we provide a brief historical introduction of Burkitt lymphoma, followed by a review of all aspects of this neoplasm including pathogenesis, clinical presentation, morphology, immunophenotype, cytogenetics and molecular findings. We also provide recent updates of this entity, including advances in our understanding of molecular pathogenesis of Burkitt lymphoma and the recent proposal in the current World Health Organization classification that the traditional epidemiologic variants of Burkitt lymphoma are better replaced by presence or absence of EBV infection. We also discuss the differential diagnosis of Burkitt lymphoma and how this neoplasm can be distinguished from reactive conditions and other aggressive B-cell lymphomas/leukemias. Given its very rapid growth and the unique treatment approach employed to treat these patients, it is important to recognize Burkitt lymphoma to facilitate appropriate therapy.

High-grade B-cell lymphomas: Double hit and non-double hit

The classification of high-grade B-cell lymphoma (HGBL) has continuously evolved over past decades. These neoplasms, as currently defined, represent about 2% of all non-Hodgkin lymphomas and patients with these neoplasms are often refractory or relapsed following standard therapy. The 5th edition of the World Health Organization classification of hematologic neoplasms (WHO-HAEM5) has refined the classification of HGBL and recognizes two types: (1) Diffuse large B-cell lymphoma (DLBCL)/HGBL with MYC and BCL2 rearrangements, with or without BCL6 rearrangements; and (2) HGBL, not otherwise specified (HGBL-NOS). WHO-HAEM5 excluded DLBCL/HGBL with concurrent MYC and BCL6 rearrangements from this category and reclassified them into DLBCL or HGBL-NOS categories respectively based on morphology. The International Consensus Classification (ICC) takes a slightly different approach. In addition to recognizing the two WHO-HAEM5 categories, they recognize HGBL with concurrent MYC and BCL6 rearrangements as a provisional entity. In this review, we provide an update of HGBL and its subgroups, focusing on their clinicopathologic features, diagnosis, molecular genetic features, and pathogenesis. Our diagnostic approach and caveats for differential diagnosis are also discussed with an emphasis on the differential diagnosis with B lymphoblastic leukemia/lymphoma.

CD38, CD39, and BCL2 differentiate disseminated forms of high-grade B-cell lymphomas in biological fluids from Burkitt lymphoma and diffuse large B-cell lymphoma

High-grade B-cell lymphomas (HGBCL) represent a heterogeneous group of very rare mature B-cell lymphomas. The 4th revised edition of the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues (WHO-HAEM) previously defined two categories of HGBCL: the so-called double-hit (DHL) and triple-hit (THL) lymphomas, which were related to forms harboring MYC and BCL2 and/or BCL6 rearrangements, and HGBCL, NOS (not otherwise specified), corresponding to entities with intermediate characteristics between diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma (BL), without rearrangement of the MYC and BCL2, and/or BCL6 genes. In the 5th edition of the WHO-HAEM, DHL with MYC and BCL2 rearrangements or THL were reassigned as DLBCL/HGBCL with MYC and BCL2 rearrangements (DLBCL/HGBL-MYC/BCL2), whereas the category HGBCL, NOS remains unchanged. Characterized by an aggressive clinical presentation and a poor prognosis, HGBCL is often diagnosed at an advanced, widespread stage, leading to potential disseminated forms with a leukemic presentation, or spreading to the bone marrow (BM) or other biological fluids. Flow cytometric immunophenotypic study of these disseminated cells can provide a rapid method to identify HGBCL. However, due to the scarcity of cases, only limited data about the immunophenotypic features of HGBCL by multiparametric flow cytometry are available. In addition, identification of HGBCL cells by this technique may be challenging due to clinical, pathological, and biological features that can overlap with other distinct lymphoid malignancies, including Burkitt lymphoma (BL), diffuse large B-cell lymphoma (DLBCL), and even B acute lymphoblastic leukemia (B-ALL). In this study, we aimed to characterize the detailed immunophenotypic portrait of HGBCL, evaluating by multiparametric flow cytometry (MFC) the expression of 26 markers on biological samples obtained from a cohort of 10 newly-diagnosed cases and comparing their level of expression with normal peripheral blood (PB) B lymphocytes (n = 10 samples), tumoral cells from patients diagnosed with B-ALL (n = 30), BL (n = 13), or DLBCL (n = 22). We then proposed a new and simple approach to rapidly distinguish disseminated forms of HGBCL, BL, and DLBCL, using the combination of MFC data for CD38, BCL2, and CD39, the three most discriminative markers explored in this study. We finally confirmed the utility of the scoring system previously proposed by Khanlari to distinguish HGBCL cells from B lymphoblasts of B-ALL. In conclusion, we described a distinct immunophenotypic portrait of HGBCL cells and proposed a strategy to differentiate these cells from other aggressive B lymphoma entities in biological samples.

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.

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.

The Clinicopathologic Features and Molecular Signatures of Blastoid High-Grade B Cell Lymphoma, Not Otherwise Specified

A small subset of high-grade B-cell lymphoma (HGBL) with blastoid morphology remains poorly understood. We assessed 55 cases of blastoid HGBL, not otherwise specified (NOS) and compared their clinicopathologic characteristics with those of 81 non-blastoid HGBL-NOS and 62 blastoid HGBL with MYC and BCL2, with or without BCL6 rearrangements (double/triple-hit lymphoma [D/THL]). Patients with blastoid HGBL-NOS showed similar clinicopathologic features to patients with blastoid D/THLs and non-blastoid HGBL-NOS, except more frequently with a history of low-grade B-cell lymphoma, bone marrow involvement, and BCL2 rearrangement (P < .05) compared to the latter. MYC rearrangement (MYC-R), detected in 40% of blastoid HGBL-NOS, was associated with aggressive clinicopathologic features and poorer overall survival, even worse than that of blastoid D/THL (P < .05). Transcriptome profiling revealed a distinct gene expression pattern with differentially expressed genes enriched in MYC and P53-targeted genes in MYC-R blastoid HGBL-NOS. Fifty-two percent of blastoid HGBL-NOS had a double hit-like signature, similar to non-blastoid HGBL-NOS (P = .73). The overall survival of the blastoid HGBL-NOS group was similar to that of the blastoid D/THL group but appeared poorer than that of its non-blastoid counterparts (P = .07). Taken together, blastoid HGBL-NOS is an aggressive B-cell lymphoma that shares overlapping clinicopathologic and genetic features with non-blastoid HGBL-NOS. MYC-R in patients with blastoid HGBL-NOS identifies a highly aggressive subgroup with distinct aggressive clinicopathologic features, unique molecular signatures, and a dismal clinical outcome.

High-grade B-cell lymphoma, not otherwise specified: a multi-institutional retrospective study

In this multi-institutional retrospective study, we examined the characteristics and outcomes of 160 patients with high-grade B-cell lymphoma, not otherwise specified (HGBL-NOS)-a rare category defined by high-grade morphologic features and lack of MYC rearrangements with BCL2 and/or BCL6 rearrangements ("double hit"). Our results show that HGBL-NOS tumors are heterogeneous: 83% of patients had a germinal center B-cell immunophenotype, 37% a dual-expressor immunophenotype (MYC and BCL2 expression), 28% MYC rearrangement, 13% BCL2 rearrangement, and 11% BCL6 rearrangement. Most patients presented with stage IV disease, a high serum lactate dehydrogenase, and other high-risk clinical factors. Most frequent first-line regimens included dose-adjusted cyclophosphamide, doxorubicin, vincristine, and etoposide, with rituximab and prednisone (DA-EPOCH-R; 43%); rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP; 33%); or other intensive chemotherapy programs. We found no significant differences in the rates of complete response (CR), progression-free survival (PFS), or overall survival (OS) between these chemotherapy regimens. CR was attained by 69% of patients. PFS at 2 years was 55.2% and OS was 68.1%. In a multivariable model, the main prognostic factors for PFS and OS were poor performance status, lactate dehydrogenase >3 × upper limit of normal, and a dual-expressor immunophenotype. Age >60 years or presence of MYC rearrangement were not prognostic, but patients with TP53 alterations had a dismal PFS. Presence of MYC rearrangement was not predictive of better PFS in patients treated with DA-EPOCH-R vs R-CHOP. Improvements in the diagnostic criteria and therapeutic approaches beyond dose-intense chemotherapy are needed to overcome the unfavorable prognosis of patients with HGBL-NOS.