Widespread in situ follicular neoplasia in patients who subsequently developed follicular lymphoma

Relapses in early-stage follicular lymphoma frequently develop via a divergent evolution from their clonally related precursor cells

Follicular lymphoma (FL) develops through a stepwise acquisition of cooperative genetic changes with t(14;18)(q32;q21)/IGH::BCL2 occurring early at the pre-B stage of B-cell development. Patients with FL typically show an indolent clinical course, remitting and relapsing with the eventual development of resistance to treatments. Interestingly, the majority of transformed FL do not progress directly from FL but originate from their clonally related lymphoma precursor (CLP) cells. To examine whether such divergent tumour evolution also underpins the relapses in patients with early-stage FL, we investigated by targeted next-generation sequencing 13 cases (stage I = 9, stage II = 4), who showed complete remission (mean: 5 years; range: 1-11.5 years) following local radiotherapy but subsequently relapsed (≥2 in 5). A clonal relationship between the diagnostic FL and relapses was confirmed in 11 cases. In six cases, common and distinct variants were seen between the paired diagnostic and relapsed lymphomas, indicating their divergent evolution from a CLP. In two cases, different B-cell clones were involved in the diagnostic and relapsed lymphomas, including one case involving two different BCL2 translocations. In the remaining five cases, the relapsed lymphoma developed via a linear progression (n = 4) or a mixed evolutionary path (n = 1). These findings may bear important implications in the routine diagnosis and management of relapsed FL. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

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.

Non-IG::MYC in diffuse large B-cell lymphoma confers variable genomic configurations and MYC transactivation potential

MYC translocation occurs in 8-14% of diffuse large B-cell lymphoma (DLBCL), and may concur with BCL2 and/or BCL6 translocation, known as double-hit (DH) or triple-hit (TH). DLBCL-MYC/BCL2-DH/TH are largely germinal centre B-cell like subtype, but show variable clinical outcome, with IG::MYC fusion significantly associated with inferior survival. While DLBCL-MYC/BCL6-DH are variable in their cell-of-origin subtypes and clinical outcome. Intriguingly, only 40-50% of DLBCL with MYC translocation show high MYC protein expression (>70%). We studied 186 DLBCLs with MYC translocation including 32 MYC/BCL2/BCL6-TH, 75 MYC/BCL2-DH and 26 MYC/BCL6-DH. FISH revealed a MYC/BCL6 fusion in 59% of DLBCL-MYC/BCL2/BCL6-TH and 27% of DLBCL-MYC/BCL6-DH. Targeted NGS showed a similar mutation profile and LymphGen genetic subtype between DLBCL-MYC/BCL2/BCL6-TH and DLBCL-MYC/BCL2-DH, but variable LymphGen subtypes among DLBCL-MYC/BCL6-DH. MYC protein expression is uniformly high in DLBCL with IG::MYC, but variable in those with non-IG::MYC including MYC/BCL6-fusion. Translocation breakpoint analyses of 8 cases by TLC-based NGS showed no obvious genomic configuration that enables MYC transactivation in 3 of the 4 cases with non-IG::MYC, while a typical promoter substitution or IGH super enhancer juxtaposition in the remaining cases. The findings potentially explain variable MYC expression in DLBCL with MYC translocation, and also bear practical implications in its routine assessment.

Divergent evolution of metachronous follicular lymphoma and extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue from a common precursor

The translocation t(14;18)(q32:q21)/IGH::BCL2 occurs at the pre-B stage of B-cell development in the bone marrow and is insufficient for malignant transformation, although it leads to the formation of in situ follicular B-cell neoplasia (ISFN). Despite that, the translocation is the genetic hallmark of follicular lymphoma (FL), it occurs infrequently in metachronous/synchronous lymphomas, including extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (EMZL), mantle cell lymphoma, and Hodgkin's lymphoma. In each of these scenarios, the two lymphomas often appear to be clonally related by analyses of IGH::BCL2 and/or rearranged IG genes. However, it remains largely unknown whether one lymphoma originates from the other or they develop independently. We studied five cases of metachronous EMZL and FL. In four cases, the two lymphomas were clonally related, as shown by identical IGH::BCL2 and/or rearranged IG genes or shared mutations. There were common and unique mutations between the paired EMZL and FL, indicating that they developed independently from a common premalignant cell population, harbouring IGH::BCL2 in three cases. Furthermore, case 1 presented with three metachronous FLs, and all of them originated from a common precursor cell population via divergent evolution. Our findings highlight the multi-malignant potential of IGH::BCL2-positive B-cells. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Clonal composition and differentiation stage of human CD30+ B cells in reactive lymph nodes

Introduction

Normal CD30+ B cells represent a distinct B-cell differentiation stage with features of strong activation. We lack an in depth understanding of these cells, because they are not present in peripheral blood and are typically very rare in reactive lymphoid organs. CD30+ B cells have been discussed as a potential precursor population for the malignant CD30+ Hodgkin and Reed-Sternberg cells in classical Hodgkin lymphoma. As CD30+ B cells can be more numerous in some cases of reactive lymphadenitis, we aimed to characterize these CD30+ B cells in terms of their differentiation stage and clonal composition, also as a means to clarify whether such CD30+ B-cell populations may represent potential precursor lesions of Hodgkin lymphoma.

Methods

We microdissected single CD30+ B cells from tissue sections of eight reactive lymph nodes with substantial numbers of such cells and sequenced their rearranged immunoglobulin (Ig) heavy chain V region (IGHV) genes.

Results

The CD30+ B cells were polyclonal B cells in all instances, and they not only encompass post-germinal center (GC) B cells with mutated IGHV genes, but also include a substantial fraction of pre-germinal center B cells with unmutated IGHV genes. In five of the lymph nodes, mostly small clonal expansions were detected among the CD30+ B cells. Most of the expanded clones carried somatically mutated IGHV genes and about half of the mutated clones showed intraclonal diversity.

Discussion

We conclude that in human reactive lymph nodes with relatively many CD30+ B cells, these cells are a heterogenous population of polyclonal B cells encompassing activated pre-GC B cells as well as GC and post-GC B cells, with some clonal expansions. Because of their polyclonality and frequent pre-GC differentiation stage, there is no indication that such cell-rich CD30+ B-cell populations represent precursor lesions of Hodgkin lymphoma.

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.

Plasma Concentrations and Cancer-Associated Mutations in Cell-Free Circulating DNA of Treatment-Naive Follicular Lymphoma for Improved Non-Invasive Diagnosis and Prognosis

Follicular lymphoma (FL) is the second most frequent non-Hodgkin lymphoma accounting for 10-20% of all lymphomas in western countries. As a clinically heterogeneous cancer, FL occasionally undergoes histological transformation to more aggressive B cell lymphoma types that are associated with poor prognosis. Here we evaluated the potential of circulating cell-free DNA (cfDNA) to improve the diagnosis and prognosis of follicular lymphoma patients. Twenty well-characterized FL cases (13 symptomatic and 7 asymptomatic) were prospectively included in this study. Plasma cfDNA, formalin-fixed paraffin-embedded (FFPE) tumor tissue DNA, and patient-matched granulocyte genomic DNA samples were obtained from 20 treatment-naive FL cases. Ultra-deep targeted next-generation sequencing was performed with these DNA samples by using a custom-designed platform including exons and exon-intron boundaries of 110 FL related genes. Using a strict computational bioinformatics pipeline, we identified 91 somatic variants in 31 genes in treatment-naive FL cases. Selected variants were cross-validated by using PCR-Sanger sequencing. We observed higher concentrations of cfDNA and a higher overlap of somatic variants present both in cfDNA and tumor tissue DNA in symptomatic FL cases compared to asymptomatic ones. Variants known to be associated with FL pathogenesis such as STAT6 p.D419 or EZH2 p.Y646 were observed in patient-matched cfDNA and tumor tissue samples. Consistent with previous observations, high Ki-67 staining, elevated LDH levels, FDG PET/CT positivity were associated with poor survival. High plasma cfDNA concentrations or the presence of BCL2 mutations in cfDNA showed significant association with poor survival in treatment-naive patients. BCL2 mutation evaluations in cfDNA improved the prognostic utility of previously established variables. In addition, we observed that a FL patient who had progressive disease contained histological transformation-associated gene (i.e. B2M and BTG1) mutations only in cfDNA. Pre-treatment concentrations and genotype of plasma cfDNA may be used as a liquid biopsy to improve diagnosis, risk stratification, and prediction of histological transformation. Targeted therapies related to oncogenic mutations may be applied based on cfDNA genotyping results. However, the results of this study need to be validated in a larger cohort of FL patients as the analyses conducted in this study have an exploratory nature.